China’s role as a big oil consumer has become a crucial factor in energy markets in recent years. Now, its role as a major producer is gaining attention as well. China is among the world’s top five oil producers, but its fields are growing depleted and are increasingly expensive to pump. The country’s leading companies are choosing to leave more of their oil in the ground and some analysts now say Chinese oil output may have peaked. China Petroleum & Chemical Corp. SNP -1.18 % , better known as Sinopec, recently said its crude production fell nearly 5% last year. Its rival, state-owned behemoth PetroChina Co. PTR -1.31 % , said oil output fell by 1.5% over the first three quarters of 2015—the company hasn’t released fourth-quarter data yet. Together, Sinopec and PetroChina account for about 75% of Chinese oil production, according to research firm Energy Aspects. As China’s […]