* State oil firm underpaid $8.3 bln from oil sales
* Billions from LNG earnings didn't reach government
* Previous reports on corruption largely ignored (Adds details, background)
By Joe Brock
ABUJA, Jan 31 (Reuters) - Nigeria's state oil firm NNPC failed to pay the government billions of dollars in earnings from 2009-2011, an audit showed on Thursday, adding to a string of reports showing mismanagement of the energy sector.
The audit by the Nigerian Extractive Industries Transparency Initiative (NEITI) - a government agency that operates as part of a global EITI scheme - found that NNPC owed 1.3 trillion Nigerian naira ($8.3 billion) from crude oil sales in the three-year period.
The firm also owed $4.84 billion in dividends and loan repayments from the Nigerian Liquefied Natural Gas (NLNG) export business between 2009-2011 and a further $3.99 billion in NLNG funds from previous years going back to 1999, the audit said.
An NNPC spokeswoman said the firm could not comment on the findings because it had not seen the report yet.
Nigeria is among the world's top 10 crude exporters, shipping around 2 million barrels per day (bpd). It is also home to the world's ninth biggest gas reserves and one of its largest Liquefied Natural Gas (LNG) export terminals.
Africa's biggest energy industry has been criticised for being corrupt for years. But audits and reports have never resulted in high-level officials being charged and have rarely prompted a change in the way revenues are managed.
NEITI said it would further investigate NNPC's rapidly escalating fuel import subsidy bill, which the audit showed rose from 198 billion naira in 2009 to 786 billion naira in 2011.
Nigeria has to import 85 percent of its refined fuel needs. It tried to end fuel subsidies in January last year but a week of public protests forced the government to partially re-instate the payments, which are the biggest single drag on the federal budget.
A parliamentary investigation following the strikes showed how "endemic corruption" in the administration of the subsidy regime had resulted in a rapid increase in payments between 2009-2011, with much of the money paid out on fuel that was never delivered.
Some small fuel marketers have been arraigned for their part in the $6.8 billion subsidy scam but no government official has been charged. NNPC is the biggest importer of fuel.
The state-oil firm receives 445,000 bpd of crude oil to refine locally but only uses 20 percent of it because Nigerian refineries are in disrepair. The rest it sells, the audit said.
NEITI said NNPC then removes subsidy from the money it earns from the crude oil sales before sending the balance to government accounts, a practise the auditor said the government should change because it left "gaps in the process".
A government-commissioned probe in November found Nigeria lost out on tens of billions of dollars in revenues over the last decades due to cut-price deals struck between foreign oil majors and government officials.
NEITI's audit said Nigeria was owed around $5.85 billion in underpaid taxes and royalties from oil and gas producers but did not name specific companies. The audit said some firms were seeking legal action on the alleged debts.
Africa's second-largest economy is growing in popularity as an investment destination but corruption remains one of the chief concerns for foreign investors.
$1 = 157.3750 naira Editing by Tim Cocks/Ruth Pitchford