Venezuela's oil shipments to China have risen to 640,000 barrels a day, around a fifth of the South American country's total crude production, underscoring growing ties between the two nations, according to Oil Minister Rafael Ramirez.

Around 264,000 barrels of those daily shipments are earmarked to pay off billions in development loans granted by the Asian giant.

"We are comfortable with that mechanism," Mr. Ramirez said, reiterating that the oil is sold to China at market price and not at a discount, as the government's detractors claim. The latest shipment figure represents a sizable 39% leap from the 460,000 barrels a day that, only earlier this year, Venezuelan officials said were being shipped to China.

During a bitterly contested presidential election, the political opposition has been critical of the government's oil-for-loans swaps with China, saying the deals have contributed to Venezuela's quickly climbing debt load. Critics also question whether Venezuela is indeed exporting oil to China at market rates, since details of the agreements have not been released to the public or vetted by the national legislature.

Opposition presidential candidate Henrique Capriles has vowed to end preferential oil deals with certain allies and has promised to stop "gifting" oil if he wins the vote.

The 40-year-old presidential hopeful, however, does not place the accords with China among the oil deals he would automatically strike, he said during a brief interview.

"The case of China is different. Though I'm sure there is some opportunity to revise the accords," Mr. Capriles said. The former congressman and state governor contends that China does not receive oil "gifts" but future oil sales. The main challenger to the re-election bid of President Hugo Chavez does not necessarily fully endorse the deals but declines to offer specify revisions without knowing the full details of the agreements, Mr. Capriles said.

On Tuesday night, President Hugo Chavez, who is looking to extend his 13-year tenure on Oct. 7, rejected the idea that his government was giving oil away to anyone. He also added the country is on track to reach its goal of raising production to 3.5 million barrels a day from 3 million at the start of the year.

The Chavez administration is banking on high oil prices this year to pay for increased government expenditures in the run-up to the elections.

Mr. Ramirez said that he expects state oil company Petroleos de Venezuela, or PdVSA, to show financial results similar to last year as the average price of the country's basket of crude oil and petroleum derivatives remains at $105.61 a barrel, just above 2011's average price of $101.06 a barrel.

PdVSA recorded a 31% increase in revenue to $124.8 billion and a 43% jump in net income to $4.5 billion in 2011, compared with the previous year.

The minister also reiterated his proposal for setting a $100-a-barrel base for the commodity and a "price band between $90 and $110 per barrel that leaves the average at $100, which we think is fair."