The world’s biggest oil companies are draining their petroleum reserves faster than they are replacing them—a symptom of how a deep oil-price decline is reshaping the energy industry’s priorities. In 2015, the seven biggest publicly traded Western energy companies, including Exxon Mobil Corp. XOM 0.27 % and Royal Dutch Shell RDS.A 1.22 % PLC, replaced just 75% of the oil and natural gas they pumped, on average, according to a Wall Street Journal analysis of company data. It was the biggest combined drop in inventory that companies have reported in at least a decade. For Exxon, 2015 marked the first time in more than two decades it didn’t fully replace production with new reserves, according to the company. It reported replacing 67% of its 2015 output. In the past, shrinking reserves could send investors […]