diff --git a/lib/vmpooler.rb b/lib/vmpooler.rb
index 70bb819..7cfacbb 100644
--- a/lib/vmpooler.rb
+++ b/lib/vmpooler.rb
@@ -10,6 +10,7 @@ module Vmpooler
   require 'time'
   require 'timeout'
   require 'yaml'
+  require 'set'
 
   %w( api graphite logger pool_manager vsphere_helper ).each do |lib|
     begin
@@ -35,15 +36,19 @@ module Vmpooler
     parsed_config[:config]['prefix']       ||= ''
 
     # Create an index of pool aliases
+    parsed_config[:pool_names] = Set.new
     parsed_config[:pools].each do |pool|
+      parsed_config[:pool_names] << pool['name']
       if pool['alias']
         if pool['alias'].kind_of?(Array)
           pool['alias'].each do |a|
             parsed_config[:alias] ||= {}
             parsed_config[:alias][a] = pool['name']
+            parsed_config[:pool_names] << a
           end
         elsif pool['alias'].kind_of?(String)
           parsed_config[:alias][pool['alias']] = pool['name']
+          parsed_config[:pool_names] << pool['alias']
         end
       end
     end
diff --git a/lib/vmpooler/api/v1.rb b/lib/vmpooler/api/v1.rb
index e6c1ea7..f9f29b3 100644
--- a/lib/vmpooler/api/v1.rb
+++ b/lib/vmpooler/api/v1.rb
@@ -20,6 +20,10 @@ module Vmpooler
       Vmpooler::API.settings.config[:pools]
     end
 
+    def pool_exists?(template)
+      Vmpooler::API.settings.config[:pool_names].include?(template)
+    end
+
     def need_auth!
       validate_auth(backend)
     end
@@ -28,25 +32,19 @@ module Vmpooler
       validate_token(backend)
     end
 
-    def alias_deref(hash)
-      newhash = {}
+    def fetch_single_vm(template)
+      vm = backend.spop('vmpooler__ready__' + template)
 
-      hash.each do |key, val|
-        if backend.exists('vmpooler__ready__' + key)
-          newhash[key] = val
-        else
-          if Vmpooler::API.settings.config[:alias][key]
-            newkey = Vmpooler::API.settings.config[:alias][key]
-            newhash[newkey] = val
-          end
-        end
+      return [vm, template] if vm
+
+      aliases = Vmpooler::API.settings.config[:alias]
+      if aliases && aliased_template = aliases[template]
+        vm = backend.spop('vmpooler__ready__' + aliased_template)
+
+        return [vm, aliased_template] if vm
       end
 
-      newhash
-    end
-
-    def fetch_single_vm(template)
-      backend.spop('vmpooler__ready__' + template)
+      [nil, nil]
     end
 
     def return_vm_to_ready_state(template, vm)
@@ -83,33 +81,31 @@ module Vmpooler
     end
 
     def atomically_allocate_vms(payload)
-      return false unless payload and !payload.empty?
-
       result = { 'ok' => false }
       failed = false
       vms = []
 
       payload.each do |template, count|
         count.to_i.times do |_i|
-          vm = fetch_single_vm(template)
+          vm, name = fetch_single_vm(template)
           if !vm
             failed = true
             break
           else
-            vms << [ template, vm ]
+            vms << [ name, vm ]
           end
         end
       end
 
       if failed
-        vms.each do |(template, vm)|
-          return_vm_to_ready_state(template, vm)
-          status 503
+        vms.each do |(name, vm)|
+          return_vm_to_ready_state(name, vm)
         end
+        status 503
       else
-        vms.each do |(template, vm)|
-          account_for_starting_vm(template, vm)
-          update_result_hosts(result, template, vm)
+        vms.each do |(name, vm)|
+          account_for_starting_vm(name, vm)
+          update_result_hosts(result, name, vm)
         end
 
         result['ok'] = true
@@ -371,12 +367,13 @@ module Vmpooler
     end
 
     post "#{api_prefix}/vm/?" do
-      jdata = alias_deref(JSON.parse(request.body.read))
       content_type :json
       result = { 'ok' => false }
 
-      if jdata and !jdata.empty?
-        result = atomically_allocate_vms(jdata)
+      payload = JSON.parse(request.body.read)
+
+      if all_templates_valid?(payload)
+        result = atomically_allocate_vms(payload)
       else
         status 404
       end
@@ -395,12 +392,21 @@ module Vmpooler
       payload
     end
 
+    def all_templates_valid?(payload)
+      return false unless payload
+
+      payload.keys.all? do |templates|
+        pool_exists?(templates)
+      end
+    end
+
     post "#{api_prefix}/vm/:template/?" do
-      payload = alias_deref(extract_templates_from_query_params(params[:template]))
       content_type :json
       result = { 'ok' => false }
 
-      if payload and !payload.empty?
+      payload = extract_templates_from_query_params(params[:template])
+
+      if all_templates_valid?(payload)
         result = atomically_allocate_vms(payload)
       else
         status 404
diff --git a/spec/helpers.rb b/spec/helpers.rb
index d28b761..292b9f4 100644
--- a/spec/helpers.rb
+++ b/spec/helpers.rb
@@ -35,6 +35,7 @@ end
 def create_ready_vm(template, name, token = nil)
   create_vm(name, token)
   redis.sadd("vmpooler__ready__#{template}", name)
+  # REMIND: should be __vm__?
   redis.hset("vmpooler_vm_#{name}", "template", template)
 end
 
@@ -73,3 +74,7 @@ def vm_reverted_to_snapshot?(vm, snapshot = nil)
     instance == vm and (snapshot ? (sha == snapshot) : true)
   end
 end
+
+def pool_has_ready_vm?(pool, vm)
+  !!redis.sismember('vmpooler__ready__' + pool, vm)
+end
diff --git a/spec/vmpooler/api/v1/vm_spec.rb b/spec/vmpooler/api/v1/vm_spec.rb
index 6a4a068..5622468 100644
--- a/spec/vmpooler/api/v1/vm_spec.rb
+++ b/spec/vmpooler/api/v1/vm_spec.rb
@@ -32,6 +32,7 @@ describe Vmpooler::API::V1 do
           {'name' => 'pool2', 'size' => 10}
         ],
         alias: { 'poolone' => 'pool1' },
+        pool_names: [ 'pool1', 'pool2', 'poolone' ]
       }
     }
 
@@ -84,6 +85,31 @@ describe Vmpooler::API::V1 do
         expect_json(ok = false, http = 404)
       end
 
+      it 'returns 503 for empty pool when aliases are not defined' do
+        Vmpooler::API.settings.config.delete(:alias)
+        Vmpooler::API.settings.config[:pool_names] = ['pool1', 'pool2']
+
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+        post "#{prefix}/vm/pool1"
+        post "#{prefix}/vm/pool1"
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
+      it 'returns 503 for empty pool referenced by alias' do
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+        post "#{prefix}/vm/poolone"
+        post "#{prefix}/vm/poolone"
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
       it 'returns multiple VMs' do
         create_ready_vm 'pool1', 'abcdefghijklmnop'
         create_ready_vm 'pool2', 'qrstuvwxyz012345'
@@ -104,6 +130,132 @@ describe Vmpooler::API::V1 do
         expect(last_response.body).to eq(JSON.pretty_generate(expected))
       end
 
+      it 'returns multiple VMs even when multiple instances from the same pool are requested' do
+        create_ready_vm 'pool1', '1abcdefghijklmnop'
+        create_ready_vm 'pool1', '2abcdefghijklmnop'
+        create_ready_vm 'pool2', 'qrstuvwxyz012345'
+
+        post "#{prefix}/vm", '{"pool1":"2","pool2":"1"}'
+
+        expected = {
+          ok: true,
+          pool1: {
+            hostname: [ '1abcdefghijklmnop', '2abcdefghijklmnop' ]
+          },
+          pool2: {
+            hostname: 'qrstuvwxyz012345'
+          }
+        }
+
+        result = JSON.parse(last_response.body)
+        expect(result['ok']).to eq(true)
+        expect(result['pool1']['hostname']).to include('1abcdefghijklmnop', '2abcdefghijklmnop')
+        expect(result['pool2']['hostname']).to eq('qrstuvwxyz012345')
+
+        expect_json(ok = true, http = 200)
+      end
+
+      it 'returns multiple VMs even when multiple instances from multiple pools are requested' do
+        create_ready_vm 'pool1', '1abcdefghijklmnop'
+        create_ready_vm 'pool1', '2abcdefghijklmnop'
+        create_ready_vm 'pool2', '1qrstuvwxyz012345'
+        create_ready_vm 'pool2', '2qrstuvwxyz012345'
+        create_ready_vm 'pool2', '3qrstuvwxyz012345'
+
+        post "#{prefix}/vm", '{"pool1":"2","pool2":"3"}'
+
+        expected = {
+          ok: true,
+          pool1: {
+            hostname: [ '1abcdefghijklmnop', '2abcdefghijklmnop' ]
+          },
+          pool2: {
+            hostname: [ '1qrstuvwxyz012345', '2qrstuvwxyz012345', '3qrstuvwxyz012345' ]
+          }
+        }
+
+        result = JSON.parse(last_response.body)
+        expect(result['ok']).to eq(true)
+        expect(result['pool1']['hostname']).to include('1abcdefghijklmnop', '2abcdefghijklmnop')
+        expect(result['pool2']['hostname']).to include('1qrstuvwxyz012345', '2qrstuvwxyz012345', '3qrstuvwxyz012345')
+
+        expect_json(ok = true, http = 200)
+      end
+
+      it 'fails when not all requested vms can be allocated' do
+        create_ready_vm 'pool1', '1abcdefghijklmnop'
+
+        post "#{prefix}/vm", '{"pool1":"1","pool2":"1"}'
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
+      it 'returns any checked out vms to their pools when not all requested vms can be allocated' do
+        create_ready_vm 'pool1', '1abcdefghijklmnop'
+
+        post "#{prefix}/vm", '{"pool1":"1","pool2":"1"}'
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+
+        expect(pool_has_ready_vm?('pool1', '1abcdefghijklmnop')).to eq(true)
+      end
+
+      it 'fails when not all requested vms can be allocated, when requesting multiple instances from a pool' do
+        create_ready_vm 'pool1', '1abcdefghijklmnop'
+
+        post "#{prefix}/vm", '{"pool1":"2","pool2":"1"}'
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
+      it 'returns any checked out vms to their pools when not all requested vms can be allocated, when requesting multiple instances from a pool' do
+        create_ready_vm 'pool1', '1abcdefghijklmnop'
+
+        post "#{prefix}/vm", '{"pool1":"2","pool2":"1"}'
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+
+        expect(pool_has_ready_vm?('pool1', '1abcdefghijklmnop')).to eq(true)
+      end
+
+      it 'fails when not all requested vms can be allocated, when requesting multiple instances from multiple pools' do
+        create_ready_vm 'pool1', '1abcdefghijklmnop'
+
+        post "#{prefix}/vm", '{"pool1":"2","pool2":"3"}'
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
+      it 'returns any checked out vms to their pools when not all requested vms can be allocated, when requesting multiple instances from multiple pools' do
+        create_ready_vm 'pool1', '1abcdefghijklmnop'
+        create_ready_vm 'pool1', '2abcdefghijklmnop'
+
+        post "#{prefix}/vm", '{"pool1":"2","pool2":"3"}'
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+
+        expect(pool_has_ready_vm?('pool1', '1abcdefghijklmnop')).to eq(true)
+        expect(pool_has_ready_vm?('pool1', '2abcdefghijklmnop')).to eq(true)
+      end
+
       context '(auth not configured)' do
         it 'does not extend VM lifetime if auth token is provided' do
           app.settings.set :config, auth: false
diff --git a/spec/vmpooler/api/v1/vm_template_spec.rb b/spec/vmpooler/api/v1/vm_template_spec.rb
index 28b85c3..3b7f055 100644
--- a/spec/vmpooler/api/v1/vm_template_spec.rb
+++ b/spec/vmpooler/api/v1/vm_template_spec.rb
@@ -32,6 +32,7 @@ describe Vmpooler::API::V1 do
           {'name' => 'pool2', 'size' => 10}
         ],
         alias: { 'poolone' => 'pool1' },
+        pool_names: [ 'pool1', 'pool2', 'poolone' ]
       }
     }
 
@@ -84,6 +85,31 @@ describe Vmpooler::API::V1 do
         expect_json(ok = false, http = 404)
       end
 
+      it 'returns 503 for empty pool when aliases are not defined' do
+        Vmpooler::API.settings.config.delete(:alias)
+        Vmpooler::API.settings.config[:pool_names] = ['pool1', 'pool2']
+
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+        post "#{prefix}/vm/pool1"
+        post "#{prefix}/vm/pool1"
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
+      it 'returns 503 for empty pool referenced by alias' do
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+        post "#{prefix}/vm/poolone"
+        post "#{prefix}/vm/poolone"
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
       it 'returns multiple VMs' do
         create_ready_vm 'pool1', 'abcdefghijklmnop'
         create_ready_vm 'pool2', 'qrstuvwxyz012345'
@@ -104,6 +130,115 @@ describe Vmpooler::API::V1 do
         expect(last_response.body).to eq(JSON.pretty_generate(expected))
       end
 
+      it 'returns multiple VMs even when multiple instances from multiple pools are requested' do
+        create_ready_vm 'pool1', '1abcdefghijklmnop'
+        create_ready_vm 'pool1', '2abcdefghijklmnop'
+
+        create_ready_vm 'pool2', '1qrstuvwxyz012345'
+        create_ready_vm 'pool2', '2qrstuvwxyz012345'
+        create_ready_vm 'pool2', '3qrstuvwxyz012345'
+
+        post "#{prefix}/vm/pool1+pool1+pool2+pool2+pool2", ''
+
+        expected = {
+          ok: true,
+          pool1: {
+            hostname: [ '1abcdefghijklmnop', '2abcdefghijklmnop' ]
+          },
+          pool2: {
+            hostname: [ '1qrstuvwxyz012345', '2qrstuvwxyz012345', '3qrstuvwxyz012345' ]
+          }
+        }
+
+        result = JSON.parse(last_response.body)
+        expect(result['ok']).to eq(true)
+        expect(result['pool1']['hostname']).to include('1abcdefghijklmnop', '2abcdefghijklmnop')
+        expect(result['pool2']['hostname']).to include('1qrstuvwxyz012345', '2qrstuvwxyz012345', '3qrstuvwxyz012345')
+        expect_json(ok = true, http = 200)
+      end
+
+      it 'fails when not all requested vms can be allocated' do
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+
+        post "#{prefix}/vm/pool1+pool2", ''
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
+      it 'returns any checked out vms to their pools when not all requested vms can be allocated' do
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+
+        post "#{prefix}/vm/pool1+pool2", ''
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+
+        expect(pool_has_ready_vm?('pool1', 'abcdefghijklmnop')).to eq(true)
+      end
+
+      it 'fails when not all requested vms can be allocated, when requesting multiple instances from a pool' do
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+        create_ready_vm 'pool1', '0123456789012345'
+
+        allow(redis).to receive(:spop).with('vmpooler__ready__pool1').and_return 'abcdefghijklmnop'
+        allow(redis).to receive(:spop).with('vmpooler__ready__pool2').and_return nil
+        allow(redis).to receive(:sadd).with("vmpooler__ready__pool1", "abcdefghijklmnop")
+
+        post "#{prefix}/vm/pool1+pool1+pool2", ''
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
+      it 'returns any checked out vms to their pools when not all requested vms can be allocated, when requesting multiple instances from a pool' do
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+        create_ready_vm 'pool1', '0123456789012345'
+
+        post "#{prefix}/vm/pool1+pool1+pool2", ''
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+
+        expect(pool_has_ready_vm?('pool1', 'abcdefghijklmnop')).to eq(true)
+        expect(pool_has_ready_vm?('pool1', '0123456789012345')).to eq(true)
+      end
+
+      it 'fails when not all requested vms can be allocated, when requesting multiple instances from multiple pools' do
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+        create_ready_vm 'pool2', '0123456789012345'
+
+        post "#{prefix}/vm/pool1+pool1+pool2+pool2+pool2", ''
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+      end
+
+      it 'returns any checked out vms to their pools when not all requested vms can be allocated, when requesting multiple instances from multiple pools' do
+        create_ready_vm 'pool1', 'abcdefghijklmnop'
+        create_ready_vm 'pool2', '0123456789012345'
+
+        post "#{prefix}/vm/pool1+pool1+pool2+pool2+pool2", ''
+
+        expected = { ok: false }
+
+        expect(last_response.body).to eq(JSON.pretty_generate(expected))
+        expect_json(ok = false, http = 503)
+
+        expect(pool_has_ready_vm?('pool1', 'abcdefghijklmnop')).to eq(true)
+        expect(pool_has_ready_vm?('pool2', '0123456789012345')).to eq(true)
+      end
+
       context '(auth not configured)' do
         it 'does not extend VM lifetime if auth token is provided' do
           app.settings.set :config, auth: false