Of all the companies behind APIs in the ProgrammableWeb directory, Google has the most APIs. The company launched its first Google API way back in 2006. The Google Search API was a SOAP and XML-based service to access search results programmatically. How times have changed, yet many Google APIs still use XML -- and a growing number have either launched with JSON support or adopted it later.
There are 61 Google XML APIs. That means that over half of Google's APIs support XML.
Since there are 33 dead Google APIs, it's interesting to compare those that have gone into the sunset by data format. Predictably, Google has killed a higher percentage of XML APIs than JSON, 31% vs 24% respectively.
Since 17 Google APIs support both XML and JSON, the popular APIs for JSON are the same as XML. Interestingly, Google acquisition Freebase API is the most popular JSON API that does not also support XML.
RSS and GData
While XML and JSON are tops, there are certainly other data formats. Two seemingly promising formats of yesteryear have been seemingly left behind by Google. There are only 8 Google RSS APIs, three of which are no longer supported at all.
If you're interested in the history of Google APIs, be sure to check out Google's first 10 APIs, all launched in 2005-2006.