FILE PHOTO: The corporate logo of the state oil company PDVSA is seen at a gas station in Caracas, Venezuela November 22, 2017. REUTERS/Marco Bello/File Photo

HOUSTON (Reuters) - Venezuela’s crude oil sales to the United States fell for a second month in a row in December, knocking the year’s average to 593,047 barrels per day (bpd), the lowest annual level since 1991, according to Thomson Reuters trade flows data.

A severe production drop in the South American country has hurt its oil exports and domestic refining, and worsened an economic recession now entering into its fifth year. Venezuela’s state-run oil company PDVSA is mired in a widespread corruption investigation that has stalled decision making.

Financial sanctions on Venezuela imposed last year by U.S. President Donald Trump’s administration have particularly affected PDVSA’s oil flows to and from the United States as the company and some of its customers struggle to get commercial credit for transactions.

The International Energy Agency, which coordinates the energy policies of industrial nations, and several analysis firms expect Venezuela’s crude output to lose another 500,000 bpd this year due to lack of investment, mounting debts, sanctions, a brain drain caused by low salaries and a new management with no experience in the oil industry.

In total, the United States received 419 crude cargoes of Venezuelan crude last year versus 530 cargoes in 2016, according to the data. The largest receivers were PDVSA’s refining unit Citgo Petroleum and Valero Energy Corp.

Chevron Corp and Phillips 66 also imported cargoes during the year, according to the data. Refining firm PBF Energy Inc stopped receiving direct supplies of Venezuelan crude from PDVSA in October after contract disagreements.

PDVSA and its joint ventures mainly sold diluted crude oil (DCO) to U.S. customers last year, a grade that mixes Venezuelan extra heavy oil with imported heavy naphtha.

The 2017 volumes reflected lower exports in recent months. Since September, shipments to the United States have not surpassed 550,000 bpd, well below the average of earlier months.

In 2016, Venezuela exported 718,365 bpd of crude to the United States from an oil production of 2.466 million bpd. Production in November - the latest number available - was 1.837 million bpd, according to figures published by OPEC.