Oil recovered somewhat on Friday, bouncing off recent lows.  The news that Syria shot down a Turkish fighter helped send prices higher.

Long-term, however, the commodity looks like it will trend lower.  It's off about a third since March, and excessive pumping will drive it further down.  And then there are concerns about the global economy.  "I think a lot of the economic worries have been priced in for the moment," said Gene McGillian of Tradition Energy to CNBC.

For the moment, markets have priced in problems in the mature economies, taking into account both the eurozone, which is headed for certain calamity, and the United States, where recovery is stalling.  One worry not fully reflected in prices, however, is the planet's largest developing nation, China.

What's there to worry about?  The consensus view is the country will grow by at least 7% this year.  That should be a cinch.  First quarter growth, according to Beijing's National Bureau of Statistics, was 8.1%, and most observers predict the economy will pick up in Q3.  The central government's growth target for the year is 7.5%, and the economy always outperforms the stated goal.  China, analysts tell us, will be the main contributor to global prosperity this year.

And that's crucial, of course, for oil.  In May, China consumed 9.4 million barrels a day, slightly more than a tenth of total daily global demand of 89.9 million barrels.

Optimists can point to the fact that oil consumption in China is rising at the moment.  Yes, oil demand increased in May, but only by 0.5% year-on-year, according to Platts.  The anemic increase is the second lowest of the year and points to trouble for the world's second-largest economy.

The low increase in China's oil demand mirrors demand for the country's other main source of energy, coal.  According to Wood Mackenzie's Rohan Kendall, there are 9.5 million tons of coal stockpiled at the Qinhuangdao port this month, surpassing the previous record of 9.3 million tons of November 2008.  Also holding record amounts of the commodity are the next three largest coal depots: Tianjin, Caofeidian, and Lianyungang.  At the same time, there are at least 30 large ships hovering off Chinese ports, waiting to deliver their cargoes of coal.  According to the China Coal Transport and Distribution Association, last month thermal coal stockpiles at utilities were up 62.5% from a year ago.

The stockpiling of coal suggests the country's economy is now contracting.  The most reliable indicator of Chinese economic activity is, according to most analysts, the production of electricity, which was up only 2.7% last month.

Yet as the New York Times reported on Friday, provincial and local officials are inflating electricity numbers reported to Beijing.  Electricity usage in Jiangsu and Shandong provinces declined more than 10% in May, according to an unnamed corporate executive cited by the paper, and electricity consumption has also fallen in locations in western China.

Falling electricity usage is consistent with the first indication from this month.  The HSBC Flash Purchasing Managers Index fell to 48.1 from the final reading of 48.4 in May, indicating further contraction in the manufacturing sector.

In these circumstances, China's oil demand will have to fall as the economy erodes further.  There are, however, two factors that should put a floor on the country's oil purchases.

First, Beijing will continue to fill its strategic petroleum reserve.  The reserve looks like it is only a sixth of its eventual size of about 700 million barrels, and this means Beijing will be a buyer for a long time to come.  Yet it's unclear whether central technocrats will be in the mood to buy—and whether they will have the cash to do so—as the contraction in their country worsens.  Moreover, Beijing may decide there is little sense in adding to its reserve if a global oil glut develops, which could happen if the world economy tanks.

Second, an insecure Beijing has leaned on its state oil companies to enter into long-term arrangements to purchase oil, and this will restrict the country from reducing its purchases to meet declining demand.  The strategy of overpaying to secure oil, which looked so smart yesterday, may end up burdening the Chinese economy in an era of decreasing need.

Of course, Beijing can always default on its arrangements with other countries.  The Chinese had no trouble in curtailing their purchases of Iranian oil in the first months of this year as they renegotiated prices with Tehran.  Look for Beijing to do the same thing with oil suppliers elsewhere.

Chinese purchasers, which drove oil prices higher in recent years, will soon force them down.  As the China Basic Materials team of Credit Suisse noted in a March 19 report, China "made the commodity cycle a lot more powerful on the way up and now can work the other way."

China, the world's second-largest user of crude, is about to depress demand for oil for a long time to come.