For all the talk about slowing growth, China’s oil demand didn’t fare too dismally last year. It likely remained stable at around 3%, even as the government doggedly pursued reform and rebalancing in favor of accelerated GDP numbers.

Yet the fact remains that analyzing oil demand in China is often a stab in the dark based on scant data. Unlike many other major consumers that release actual consumption data, China’s statistics offer no such transparency.

Oil product sales figures are not available on a national level, while inventory data is deemed a state secret and not released. Even refining capacity is often a moving target.

Therefore, most China watchers usually rely on apparent demand figures, calculated by adding net oil product imports to refinery throughput–both of which are official data–but which ignore any inventory changes. However, this can have a major impact on demand, particularly when growth has slowed compared to a decade ago. It even contracted year-on-year in certain months last year.

Platts estimates China’s apparent oil demand to have grown 3% from January to November — the latest data available — to an average 9.81 million b/d. However, based on some analyst estimates, China’s oil product stocks had fallen to the lowest level in a year at the end of November, suggesting that some real consumption was not captured in apparent demand figures.

In particular, gasoil apparent demand over January to November contracted by 0.2% year on year to an average 3.5 million b/d. But during the same period, commercial gasoil stocks fell nearly 12%, according to estimates based on monthly polls done by the Xinhua-run China Oil, Gas and Petrochemical newsletter. An inventory draw of that magnitude would appear to show more robust demand.

The issue of China’s “missing” barrels was underscored last year when the International Energy Agency said it would take into account inventory data–whether obtained officially or anecdotally–in its calculation of China’s oil demand.

Last year, there also emerged a new trend: significant biodiesel imports, a consequence of a consumption tax holiday granted to importers. Traders seized on this cost advantage and brought in large amounts of what they called biodiesel — in many cases with only a minimum 3% biofuel content — from Southeast Asia, and which they sold as conventional gasoil in the domestic market.

Beijing-based consultancy 3E estimates China’s biodiesel import last year to have hit 1.5 million mt, compared with just 200,000 mt-300,000 mt in previous years. But tax authorities have since cottoned to those import numbers, and last month extended the existing Yuan 941/mt ($155/mt) consumption tax on gasoil to biodiesel, which likely means these imports are unlikely to be sustained this year.

Given the stagnant growth in gasoil witnessed last year, and its importance in the economy, there is room for upside in 2014. Overall, the prognosis this year is similar to 2013, with oil demand growth plodding along at 3%-4%.

But set against the backdrop of re-emerging OECD oil demand—particularly in the US–as well as an increasing shift in focus to other economies such as Indonesia, Thailand, Vietnam and the Philippines to prop up Asian demand growth, China’s importance as a contributor to global growth could fade.