By LIAM DENNING

Not many institutions can look back on a year of stability with the added bonus of not having had to do much for it. OPEC can. Yet the new year will likely prove more taxing for the Organization of Petroleum Exporting Countries.

In 2010, the average OPEC oil price rose 26.5%. But that increase was pretty steady. The standard deviation of prices, measuring variance, was just $5.20, or 6.7%, of the average price of $77.25. That's the most stable it has been in the past five years and well below the 30.1% recorded in 2008, when oil prices peaked.

All this happened even though OPEC, which produces about 40% of the world's oil and natural-gas liquids, hasn't changed its effective production quotas since January 2009. This passiveness has helped persuade several Wall Street banks to raise their estimates for oil prices in 2011. Goldman Sachs, for example, predicts $100 a barrel on average, on a par with 2008 and 25% above 2010. Yet if OPEC has learned anything from the experience of 2007 and 2008, it will act to moderate such exuberance, rather than stoke it. Triple-digit oil prices were lucrative but short-lived, helping to push the industrialized world into recession.

America's oil bill was equivalent to 4.8% of gross domestic product in 2008, crudely calculated by multiplying the average oil price by consumption. At more than double the 2.1% average of the prior 20 years and the highest since 1982, this strained the economy. Using forecasts from the International Monetary Fund and the International Energy Agency, $100 oil in 2011 would equate to an uncomfortably similar 4.6% of GDP.

In response, the U.S. is making efforts to structurally reduce demand, such as pushing more strongly for electric vehicles. Despite a recovery in demand this year, Americans are set to burn about 400,000 barrels a day less than they did in 2008 and 1.7 million barrels less than in 2005, when their appetite peaked.

Hence OPEC's interest in not merely capping spikes, but repeating 2010's trick of keeping prices stable. It won't be easy, given several conflicting price indicators. U.S. oil inventories have fallen sharply in recent months. But they remain high compared with historical levels. Falling imports suggest supplies were run down ahead of the year end to minimize taxes rather than because of surging demand.

In economic terms, weak housing and employment data undermine a strong U.S. rebound. Meanwhile, China, the biggest source of growth in global oil demand, is trying to curb rising inflation, raising the risk of a slowdown.

Cross-currents in currency markets are another complication for OPEC. Lax monetary policy has helped push investors toward commodities such as oil as a hedge against a weakening dollar. Yet the euro zone's upheaval, and currency controls spreading across hot-money targets like Brazil, help the dollar. Some of the same Wall Street banks predicting higher oil prices also tout U.S. stocks as winners in 2011, suggesting more dollar buying.

Further complicating OPEC's calculations is Iraq. Excluded for now from the cartel's quota system, Iraq wants to increase output from its reserves, the world's fourth largest, according to BP. Reaccommodating those extra barrels within the OPEC system will require sacrifice from existing members—never an easy prospect.

Still, OPEC at least has more power to smooth supply and demand. Its spare capacity has almost tripled since 2008 to about six million barrels a day. Crédit Agricole reckons using just 500,000 barrels a day, or less than 10% of that buffer, would keep the global oil market comfortably supplied in 2011. If OPEC is interested in its long-term health, that should be its aim. Fans of an oil price super-spike, beware.

Write to Liam Denning at liam.denning@wsj.com

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