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The gap between certified and real-world passenger vehicle emissions is widening and has driven vehicle policy transitions in the US and in Europe, particularly in the wake of emissions measurement scandals. Since carbon dioxide emissions are highly correlated with fuel consumption (FC), fuel consumption regulation is a useful policy instrument to combat climate change. Although the Chinese government set fuel economy standards in 2004, like many countries it does not conduct testing to confirm real-world FC rates comply with the standards. This paper employs a dataset of real-world FC measurements self-reported by over 1 million vehicle owners in China between 2008 and 2017 through a dedicated mobile phone application. By comparing this user-generated FC data with FC certification, the study provides an indication of discrepancies of FC gap and its characteristics, including: vehicle model year, transmission type, segment, weight bin, and market share. The study finds that while average certified FC decreased by 15% between 2008 and 2017, real-world FC remained unchanged, resulting in FC gap increase from 12% to 30%. The paper concludes that use of a local test-cycle, authoritative data collection, and stronger enforcement, may be useful policy tools for reducing China's real-world vehicle energy consumption.