During the first six months of 2016, the world's 10 largest oil and gas companies generated $1.84 trillion in total sales, already 59.5% of the $3.09 trillion in revenue reported by the 10 largest producers in 2015. A large part of the revenue increase owes to the steady uptick in crude oil prices, from $26.11per barrel in mid-February to $51.23 per barrel in early June, infusing the struggling oil sector with some much-needed relief.

The United States is home to two of the top 10 revenue-generating oil companies of 2016, as well as five of the top 25. China's state-backed enterprises claim the top two spots, and Russia also has two top producers. The Netherlands, the United Kingdom, France and Brazil each are represented by one company in the top 10. (See also: The 5 Biggest Chinese Oil Companies)  

1. Sinopec-China Petroleum

The China Petroleum & Chemical Corp. (SNP), also known as Sinopec-China or simply Sinopec, generated $283.6 billion in revenue between January 1 and June 30, 2016. A state-owned energy company based out of Beijing, Sinopec employs more than 810,000 people and enjoys the full support of the Chinese government.

Share prices for SNP rose steadily during the period, opening the year just shy of $60 and ending June at $72. Share growth was fueled by impressive earnings in the first quarter and the strength of its refining process, which Sinopec was able to rely on during periods of falling crude prices.

2. China National Petroleum

China National Petroleum Corp., or CNPC, the top revenue-producer of 2015, ended the January - June period with $274.6 billion in net revenue. CNPC slogged through a tumultuous 2014 and 2015 in the wake of President Xi Jinping's anti-corruption crusade, during which the company listed no official general manager for 16 months, and several former executives were charged and indicted for corruption and bribery.

3. Royal Dutch Shell

Royal Dutch Shell plc (RDS-A), more commonly called Shell, brought in $264.9 billion during the first six months of 2016. The Dutch-British hybrid is the largest nongovernmental oil company in the world, but underwent a very difficult 2015 amid shallow commodity prices — share prices fell almost 40% between October 2015 and January 2016. The company rebounded some in the first and second quarters, and the stock reached $55 per share again in June for the first time in nine months. Shell also completed a $52-billion acquisition of BG Group plc in February, a move which should provide greater access to deepwater oil reserves in Brazil. (See also: Is Royal Dutch Shell's Russia LNG Project Viable?

4. Exxon Mobil

The largest American oil corporation is Exxon Mobile Corp. (XOM), which is actually the largest publicly traded oil and gas company when measured by market value. Exxon generated $236.8 billion in revenue between January1 and June 30. Share prices increased markedly during the period, climbing from around $78 to above $90, a price point last achieved in February 2015.

5. BP

BP plc (BP), formerly British Petroleum, appears to have moved past the Deepwater Horizon spill after settling a $20.8-billion claim in July 2015. It generated $218.7 billion in the first half of the year, providing much-needed revenue to a company with a shakier balance sheet than most of its petroleum rivals. Stock prices remain near five-year lows, but stronger commodity markets in 2016 offer some relief.

6. Total

France-based Total SA (TOT) ended June with $143.4 billion in revenue year-to-date (YTD). The company hopes to expand into oil reserves off the coast of Sri Lanka later in the year, although progress depends on a joint study between the company and the Sri Lanka government.

7. Chevron

The second largest American oil producer, Chevron Corporation (CVX), had generated $129.9 billion in sales by the end of June. The first half of the year was strong for stockholders, who saw CVX prices climb from approximately $90 in January, to almost $105 before July. Mixed results from the second quarter were published in July, however, triggering a minor sell-off.

8. Gazprom

Gazprom PAO (OGZPY), a Russian oil company, is responsible for more than one quarter of continental Europe's gas supply. Total revenue from the first half of the year was $102.1 billion, and the company needs to produce a strong second-half to offset poor performances in 2014 and 2015. Soft commodity prices and geopolitical turmoil struck Russian producers particularly hard in recent years.

9. Petrobras

The state-run Petroleo Brasileiro SA (PBR), also referred to as Petrobras, generated revenues of $96.3 billion through June. Brazil's most important corporation has been in the news for all of the wrong reasons — corruption, bribes, kickbacks and other infamous political intrigue. Financial performance has been remarkably sturdy despite it all, with climbing share prices and record-high production in May.

10. Lukoil

Russia's number two oil producer, Lukoil PAO posted revenues of $90.4 billion through June, despite ailing from international sanctions for Russia's involvement in Ukraine and Crimea. Lukoil hopes for access to Iranian oil reserves in coming years, but prospects remain muted until political pressures dampen.