Q1.12: 1.4M / 3.4M Q2.12: 2.1M /2.3M Q3.12: 4.3M / 5.4M Q4.12: 8.2M / 7.0M Q1.13: 12.9M / 7.3M Q2.13: 19.3M / 8.1M 2013 (total): 104M / 56M Q1.14: 45.6M / 52.2M Q2.13: 56.9M / 108.8M
Rev grew faster than losses consistently all through 2012 and 2013 which is really amazing (2013 is when Uber jumped from a 330M valuation to a 3.5B valuation so investors noticed too)...then losses abruptly charged ahead in 2014 (see data pulled below).
Uber launched China in Q1 of 2014 - they are basically betting huge on China / India, and smartly being very clear to their investors that the $$ is for that very costly cause, so they can earmark the cash they are burning for international expansion as "meant to be burned." Also, if the bet goes the wrong way, they can (sort of) cleanly write it off as a failed (billion dollar) project, and ask investors to focus on their (hopefully by then) cash-cow business in the US.
Burn is all about international expansion, which is SUPER expensive, especially at the rate they are attempting. There is an insane learning curve that costs a lot of money to get on the other side of (hiring, culture, regulations, consumers, marketing are all different in each country - not to mention the fact that local competitors have all those in line already!) - look at pretty much any major US company that has attempted to succeed in China.
Good luck!