sector firms generally lost ground, especially in the top tiers. Exxon Mobil was the exception, holding on to its No. 3 position. Comparing results across the past decade shows that as a group, the top private oil companies now account for a smaller global share of the six ranking criteria than they did before the mega-mergers that created them. Private firms still hold six of the top 10 spots just as they did in 2007. However, Saudi Aramco, Iran's NIOC, Venezuela's PDV and CNCP of China hold four of the five top rankings. PIW's annual ranking is the result of a perennial benchmark survey recognized industry-wide as the leading source of comparative performance assessments on all the world's oil companies. Operational data from more than 130 companies is used. PIW's system of ranking tends to favor NOCs with large oil and gas reserves, and to favor integrated concerns over companies that specialize in one industry sector.
