It is that time of the year when millions of Chinese have crisscrossed their country to be with their families for the Lunar New Year festivities, joining what has been tagged as the world's largest human migration.

The phenomenon gets its fair share of media coverage and this year the star has been the China's high-speed railway network.

Having arrived on the scene only 10 years ago -- the first dedicated high-speed passenger train, between the cities of Beijing and Tianjin, was opened in 2008 -- China now boasts the world's largest HSR network.

The trains are not only transforming Chinese economy and travel but are also starting to chip away at oil use in the world's second largest consumer and biggest source of fuel demand growth. The impact is being felt primarily on jet fuel and gasoline consumption. The trains, running at roughly 200-350 km/hour, provide an economical and often more reliable alternative to air travel.

State-owned oil giant China National Petroleum Corporation recently cited HSR among a host of changes including electric cars and the sharing economy as factors crimping Chinese gasoline demand growth.

China's oil consumption is estimated to have risen by 5.5% year-on-year to around 11.8 million b/d in 2017. However, the growth is expected to decelerate to around 4.2% in 2018, according to Platts China Oil Analytics. That is incremental consumption of around half a million barrels per day. Fuel substitution due to rising use of the cleaner-burning natural gas, increasing fuel efficiency and tighter environmental regulations are also whittling away Chinese oil consumption growth.

Yet, China continues to be cited as the main character in the strong global oil demand growth story that has underpinned the rally in crude prices since the fourth quarter of last year.

The strong global oil consumption narrative surprisingly remained intact through the global financial markets turmoil unfolding since the start of February.

The fears over accelerating inflation and the potential headwinds to global economic growth, which sparked a rout in equity markets across the world starting February 2, are not being viewed as crimping oil consumption. At least not yet.

Crude prices ended their months-long bull run and took a tumble in the massive stock markets sell-off as investors became risk-averse.

The U.S. Energy Information Administration, among the closely-watched forecasters of global supply and demand balances, is the most bullish on global oil consumption in 2018. The agency predicted a strong annual growth of 1.7 million b/d in world petroleum and liquid fuels demand in its February Short Term Energy Outlook report, surpassing the 1.55 million b/d increase it estimates for 2017.

Some 1.3 million b/d or three-quarters of the projected rise in consumption would come from non-OECD countries, according to the EIA.

Of the estimated 51.4 million b/d of non-OECD liquid fuels consumption in 2017, just under half was consumed in four countries -- Brazil, China, India and Russia -- the agency noted.

OPEC is also relatively sanguine about the increase in oil consumption and projected an annual increase of 1.59 million b/d in 2018, almost on a par with the 1.6 million b/d growth it estimates for 2017. Non-OECD countries, led by China and India, would contribute about 1.26 million b/d or 79% of the incremental demand, the oil producers' organization predicted.

A "close linkage" between economic growth in these countries and their appetite for oil is expected to continue, "at least for the short term," according to OPEC. The organization gave a nod to fuel substitution across OECD Americas, Asia Pacific and the Middle East as a factor "limiting" the rise in oil consumption but that did not detract from its strong overall demand growth expectations.

The International Energy Agency, the Paris-based energy policy advisor to the developed world, had been cautious in recent months on its demand outlook, citing the dampening effect of higher prices. However, the IEA also joined the party of demand optimists in its latest monthly oil market report, raising its growth forecast for 2018 to 1.4 million b/d from the previous 1.3 million b/d. It pointed out that a weaker dollar was partly offsetting higher crude prices. The IEA projection still remains conservative compared with its peers and represents a slowdown from last year's growth of 1.6 million b/d.

India is the world's third largest oil consumer after the U.S. and China and its demand is also on a steep upward incline. However, with an average consumption of around 4.3 million b/d in 2017, according to the latest government data, its appetite is much smaller than China's and it is a far smaller contributor in absolute terms to the word's rising use of oil.

India recorded a modest annual growth of 2.5% in its 2017 oil demand. It does not appear to have been dented by higher crude prices -- consumption over October 2017 to January 2018 was in fact 2.9% higher than the January-September 2017 period -- and does not face the kind of paradigm shifts underway in China's energy mix. However, 2-3% annual growth is par for the course, which means a paltry contribution of around 130,000 b/d to global consumption from India.

If China and India, the biggest engines of global oil demand growth, are expected to add only about 600,000-650,000 b/d in incremental use this year, one wonders where the remaining 1 million b/d or more of the projected increase for 2018 will come from.

Factoring in structural changes in global oil demand - such as China's investment in high-speed rail - presents a major challenge. Alternative energy sources are also liable to be underestimated because they are growing from a small base and appear scattered and segmented. We should be vigilant about small changes that snowball into a big shift, driven by policy or a technological leap.

Vandana Hari is the founder of Vanda Insights, which tracks energy markets. She has two decades of experience providing essential intelligence on the energy commodities sector.