diff --git a/.travis.yml b/.travis.yml
index ffda774..9b941c0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,4 +5,5 @@ env:
   global:
   - secure: Dx2pqzulcauIhVXEqQoNbnwm/EZzam9smHyBd1sPHnnOt5OgikYqnZ5dJOq8gh9wCRCHt1c64NSW0g/04VDofqpBGFifL4eO/c1ZtDioTG4LT+aPXLkt0S7VXP0r2J29JyvcVMBgTi3WRQdBDk4Pd1kYgQlASGSctQmK+Cqw3Jc=
   - secure: K8Uy8SoQN8S9WuFbeZFBID6XLa7ecgzzB6HoETk91BYJccXTv+VrccnbQ6XYO2cFa5aZyL7QnQjzMRfhjofypr1jvOjVoegfulUGhveypUzEQ1ylnCA8V0bBPHuvMN76ut5fJuUfD49j5dcFjtrdiollZVUiVW1TKjzpJKA4fi0=
-  - secure: dpj8ThIN7WHFqis/Sy3K2eyI34gjzAyqQcsLy1uz5fM46reSJ6/TMurl12jgPLNototlox6T+HxLTmegu4j3O7JmUeQDAR4S+2nwPbvZmC/s8APKPca5fOEJ2iW8Fyp5MKC13fUjvq+qm/CCr8o0Dmz3QdjIdftDxBsspUGlpEA=
+  - secure: PubBxjOCOwDBzTthw7ORFCd9elZi4V2/KXi1Nnrs/oz6sNWyXC2//JLJXSBFe5GwSIt8bngbNWuRcS4ckhn0DAPgPRePDtLQ+HzHDW7noFihG3lbHwamp/wXwVQZl18vBqjntt8XoN3UtV8HgoHBV5L5HuL4rtCyMcarkxSVFnI=
+  - secure: N8fuPmTG2oO51NG7gmulHHhc32Qb3yXS4La9uYjqSkhezhNQDJVpURnjPlXSviC1JmSA3C5TzbJpzSAb80EBAhoyIQmm/G9V+c20eijL+XTs/JYvIAUyz6wqfrtYNMlY1WwYTFmBwzyax+KYij0mguF7uawsuTgTbHGMHBRBdRQ=
diff --git a/README.md b/README.md
index 181e923..0587e20 100644
--- a/README.md
+++ b/README.md
@@ -3,4 +3,4 @@
 Conveniently produce authorized [imgflo](https://github.com/jonnor/imgflo) URLs.
 
 ## Running tests
-Set environment variables for `IMGFLO_KEY`, `IMGFLO_SECRET`, and `IMGFLO_TOKEN` then run `npm test`.
+Set environment variables for `IMGFLO_KEY`, `IMGFLO_SECRET`, `IMGFLO_TOKEN_01`, and `IMGFLO_TOKEN_02` then run `npm test`.
diff --git a/index.coffee b/index.coffee
index 26c52c0..08a9f19 100644
--- a/index.coffee
+++ b/index.coffee
@@ -9,9 +9,12 @@ path = require 'path'
 # @param graph [String] The name of the imgflo graph.
 # @param params [Object] The parameters to pass to imgflo.
 # @option params input [String] The input URL to pass to imgflo.
+# @param format [String] The desired format of the resulting image. e.g. 'jpg'
+#   or 'png'. If not specified, the extension of the file provided as input is
+#   used.
 # @return [String] The imgflo URL.
 #
-imgflo = (config, graph, params) ->
+imgflo = (config, graph, params, format) ->
   throw new Error 'imgflo config object not provided' unless config?
 
   {server, key, secret} = config
@@ -28,6 +31,9 @@ imgflo = (config, graph, params) ->
   extension = path.extname(input).match(/^\.(\w+)/)[1]
   return input if extension is 'gif'
 
+  format ?= extension
+  graph = "#{graph}.#{format}" if format?
+
   query = "?#{qs.stringify(params)}"
   token = MD5 "#{graph}#{query}#{secret}"
 
diff --git a/spec/imgflo-url.coffee b/spec/imgflo-url.coffee
index e05f5d7..575b2ec 100644
--- a/spec/imgflo-url.coffee
+++ b/spec/imgflo-url.coffee
@@ -118,16 +118,39 @@ describe 'imgflo-url', ->
 
   describe 'with imgflo params', ->
 
-    it 'should produce a URL', ->
-      config =
-        server: 'https://imgflo.herokuapp.com/'
-        key: process.env.IMGFLO_KEY
-        secret: process.env.IMGFLO_SECRET
-
-      url = imgflo config, 'gradientmap',
-        input: 'https://pbs.twimg.com/media/BlM0d2-CcAAT9ic.jpg:large'
-        color1: '#0A2A2F'
-        color2: '#FDE7A0'
-        srgb: true
-
-      expect(url).to.equal "https://imgflo.herokuapp.com/graph/#{process.env.IMGFLO_KEY}/#{process.env.IMGFLO_TOKEN}/gradientmap?input=https%3A%2F%2Fpbs.twimg.com%2Fmedia%2FBlM0d2-CcAAT9ic.jpg%3Alarge&color1=%230A2A2F&color2=%23FDE7A0&srgb=true"
+    context 'not specifying an image format', ->
+
+      it 'should produce the correct URL', ->
+        config =
+          server: 'https://imgflo.herokuapp.com/'
+          key: process.env.IMGFLO_KEY
+          secret: process.env.IMGFLO_SECRET
+
+        params =
+          input: 'https://pbs.twimg.com/media/BlM0d2-CcAAT9ic.jpg:large'
+          color1: '#0A2A2F'
+          color2: '#FDE7A0'
+          srgb: true
+
+        url = imgflo config, 'gradientmap', params
+
+        expect(url).to.equal "https://imgflo.herokuapp.com/graph/#{process.env.IMGFLO_KEY}/#{process.env.IMGFLO_TOKEN_01}/gradientmap.jpg?input=https%3A%2F%2Fpbs.twimg.com%2Fmedia%2FBlM0d2-CcAAT9ic.jpg%3Alarge&color1=%230A2A2F&color2=%23FDE7A0&srgb=true"
+
+
+    context 'specifying an image format', ->
+
+      it 'should produce the correct URL', ->
+        config =
+          server: 'https://imgflo.herokuapp.com/'
+          key: process.env.IMGFLO_KEY
+          secret: process.env.IMGFLO_SECRET
+
+        params =
+          input: 'https://pbs.twimg.com/media/BlM0d2-CcAAT9ic.jpg:large'
+          color1: '#0A2A2F'
+          color2: '#FDE7A0'
+          srgb: true
+
+        url = imgflo config, 'gradientmap', params, 'png'
+
+        expect(url).to.equal "https://imgflo.herokuapp.com/graph/#{process.env.IMGFLO_KEY}/#{process.env.IMGFLO_TOKEN_02}/gradientmap.png?input=https%3A%2F%2Fpbs.twimg.com%2Fmedia%2FBlM0d2-CcAAT9ic.jpg%3Alarge&color1=%230A2A2F&color2=%23FDE7A0&srgb=true"