Venezuela PDVSA's 2011 revenues up 35 pct- oil minister

* Revenues increasing, but PDVSA borrowing heavily

* Company plans to make hefty investments this year

* PDVSA aims to boost oil output in 2012 to 3.5 mln b/d

CARACAS, Feb 9 (Reuters) - Venezuela's state-run oil company PDVSA saw its revenues increase by 35 percent in 2011 due to high oil prices, the OPEC country's energy minister said on Wednesday.

Even though revenues increased to nearly $128 billion, the South American country's flagship oil company owes money to its suppliers and has borrowed heavily in recent years. PDVSA issued bonds worth $10.3 billion in 2011.

"We've got an investment plan worth $236 billion for the 2013 to 2015 period. No one pays for an investment plan with proceeds ... One has to ask for loans, and that's what we're doing," said Energy Minister Rafael Ramirez, who also is president of PDVSA.

PDVSA boosted issuance in 2011 to raise cash in the run-up to the presidential election in October in which socialist President Hugo Chavez faces one of his tightest ever elections. Analysts expect the company to issue more debt this year.

According to a preliminary report on the company's financial performance last year, PDVSA's reserves increased by 14.7 percent in 2011 to $174 billion, Ramirez told state TV.

Revenues increased, because Venezuela's basket of crude oil and refined products traded last year at $101.06 per barrel on average, a 40.4 percent increase from the previous year.

PDVSA's outstanding debt reached nearly $35 billion by end-2011, a 40 percent jump from the previous year, a company report released in January showed.

Ramirez said PDVSA made investments worth $10 billion in 2011, well below the $18.36 billion it had planned to invest.

"This year we'll invest $15 billion additionally ... to produce oil and in our refineries," Ramirez said.

PDVSA has vowed to end the year producing 3.5 million barrels per day, 500,000 bpd more than in 2011. The increase would come mainly from projects in the Orinoco oil belt, where the company plans to produce 470,000 bpd.

Venezuela is pinning its hopes for reviving its stagnant oil sector on a string of ambitious joint-venture projects with foreign companies in the region, which is one of world's biggest mostly-untapped hydrocarbon reserves.

PDVSA has a majority stake in each Orinoco project, which include partnerships with Chevron, Repsol, Eni , Rosneft and other major energy companies.