* Government upholds tax, partial gas price caps
* Gas companies worried about financial impact, instability
* Delaying projects plays into Gazprom's hands
BUCHAREST, April 1 (Reuters) - Romania's new energy regulations risk undermining plans by companies to develop big offshore gas projects in the Black Sea, putting billions of dollars of revenue at risk and squandering a chance to challenge Russia's Gazprom in the region.
Oil industry officials have warned the changes, which include a cap on some gas prices for local producers until 2022 and a 2 percent turnover tax on all energy firms bar state-owned coal-fired power plants, could slash investment plans.
OMV Petrom, which is developing a Romanian gas field with ExxonMobil, said key conditions for the project were still not in place while Black Sea Oil & Gas, controlled by private equity firm The Carlyle Group, warned it could pull out of another project if the rules remain.
The European Commission also told Romania in March that gas export restrictions and regulated prices probably contravene EU rules and could be challenged by Brussels.
Most of the new measures, first announced in an emergency decree in December, were confirmed on Friday.
The government made a last-minute concession, eliminating a cap on gas prices for industrial consumers. That means producers only have to sell about a third of their output at a fixed price - to households and heating plants - rather than more than half.
But the concession was not enough to placate the companies, given that the turnover tax and new export restrictions approved last year remain in force, coupled with the risk the state could simply shift the goal posts again.
Romania now risks delaying offshore gas projects and playing into the hands of Russia, which blocked Ukraine from exploring its Black Sea resources by occupying Crimea, analysts said.
"Postponement doesn't benefit anyone, not the state, consumers, the economy, investors," said Razvan Nicolescu, executive lead advisor in Deloitte's energy and resources division in Bucharest. "The only winner is Gazprom, the sole gas provider in the region."
Romania's Black Sea gas has the potential to challenge Gazprom's dominant role in central and eastern Europe, diversify gas supplies and bring the Romanian government revenue of $26 billion by 2040, according to the consultancy.
Romania's offshore gas reserves are estimated at 200 billion cubic metres. Russia, meanwhile, has proven reserves of 35 trillion cubic metres, according to BP's statistical review.
But while German consumption alone would empty the Romanian gas fields in two years, they could cover the combined 2017 demand of Romania, Bulgaria, Serbia, Hungary and Moldova for more than six years.
"Any cubic metre of gas produced in Romania means one less cubic metre produced and sold by Russia. Access to markets and a market share as high as possible are very important economic stakes," said Nicolescu.
Several gas producers have spent upwards of a decade and billions of dollars preparing to tap Romania's Black Sea gas, but they were blindsided by the government decree. Lawmakers also approved export restrictions on offshore gas producers.
The ruling Social Democrats, gearing up for four elections this year and next, have said the gas price cap was designed to keep tariffs low for domestic users.
"As we have said before, we want to protect the household consumer," Energy Minister Anton Anton said on Friday.
Black Sea Oil & Gas (BSOG) decided earlier this year to press ahead with plans to extract an estimated 10 billion cubic metres of gas from shallow waters - given the amount of money it has already invested.
But CEO Mark Beacom told Reuters the changes undermined the willingness of investors to move forward and were contrary to earlier assurances and legal provisions provided by the state.
"The new proposed measures taken by the government are not the best way to protect vulnerable consumers and are not sufficient to mitigate all the harmful measures recently put in place," he said on Monday.
Beacom said the entire emergency decree should be revoked, as well as additional fees and export restrictions brought in by parliament last year.
"There are always deal breakers in many different areas that could cause the investment to be terminated," he said in March.
"We look forward to having a constructive engagement with the relevant authorities to seek resolution on these issues but do not exclude the possibility of pursuing a legal course of action should such engagement not result in a positive outcome."
ExxonMobil and OMV Petrom, controlled by Austria's OMV, had planned to give the final green light for their deep water Neptun project last year, having spent nearly $2 billion to prepare for production at one of the EU's most significant natural gas deposits.
The project is now on hold.
OMV Petrom chief executive Christina Verchere said on Friday that removing the gas price cap for industrial customers answered some but not all of the industry's concerns and further talks were needed.
"Development of the Black Sea is a huge opportunity for both OMV Petrom and Romania, however, key requirements are currently not in place," she said. "Consultation with the business environment, predictability and legislative and fiscal stability are the foundation for stimulating investment."
ExxonMobil spokeswoman Julie King said the company was looking forward "to continuing our discussions with the Romanian government, parliament and relevant institutions as project evaluations continue".
According to a study commissioned by Romanian oil producers (ROPEPCA), the measures would cost the government $540 million in taxes a year and slash investment and production.
While Romania is almost energy independent - it only gets 10 percent of its needs from Russia - gas imports in the first month of 2019 were roughly 60 percent higher than a year ago, data from gas pipeline operator Transgaz showed.
"It is a negative message for the business sector in general, and the result is a feeling of uncertainty and distrust," ROPEPCA told Reuters.
"Major infrastructure and development projects, both on and offshore will most likely be suspended."
In March, Transgaz shareholders rejected its 1.9 billion euro ($2.1 billion) investment programme, which includes works on an EU-backed pipeline connecting Bulgaria, Romania, Hungary and Austria (BRUA) as well as a domestic pipeline to transport future offshore gas production.
A sore point for gas producers is the obligation to sell gas at 68 lei ($16) per megawatt hour until Feb. 2022, about 15 percent lower than the estimated average market price.
While only capping prices for some gas consumers takes some of the sting out of the measures, energy companies said enforcing it solely for producers but excluding distributors was discriminatory as they could pass on their costs to households.
"You can look after the vulnerable customer while at the same time not taking it at the cost of energy supply that you want on the market," OMV Petrom's Verchere has said. ($1 = 4.2269 lei) ($1 = 0.8906 euros) (Reporting by Luiza Ilie in Bucharest and Kirsti Knolle in Vienna; additional reporting by Gary McWilliams in Houston; editing by David Clarke)