NEW YORK (Reuters) - Companies with weak balance sheets are discovering that hedges against oil price moves can be almost as punishing as this summer’s leap in crude costs.

A general view shows the Ensco 8500 deepwater submersible drilling rig at a Keppel shipyard in Singapore in this June 28, 2008 file photo. REUTERS/Vivek Prakash

Physical oil trader SemGroup LP told its lenders this week it may file for bankruptcy after margin calls on hedges designed to protect its 500,000 barrels per day business from a fall in oil prices gobbled up its cash reserves.

SemGroup's publicly traded subsidiary SemGroup Energy Partners LP SGLP.O disclosed its privately held parent's financial troubles late on Thursday.

Traders are required to post a margin, a percentage of their position in cash, to guarantee they will meet their obligations. When the price of a futures contract rises, traders who are short the contract receive a margin call from the exchange requiring them to post even more cash.

“It’s a classic producer squeeze,” said John Kilduff, senior vice president at MF Global in New York. “They have the oil and assets in the ground but they have to make these real-time margin calls.”

The high cost of oil and the growing volatility of oil prices have created headaches for a wide range of companies, particularly airlines and freight companies that depend on affordable fuel.

Energy analysts said more liquidity problems are likely to surface in the wake of the torrid rally since April that pushed oil prices up 45 percent to a record $147.27 a barrel.

Companies facing the biggest threat right now could be those that took short positions on crude, experts said. Independent oil and gas producers, companies like SemGroup that buy and trade oil, and refiners head the list of potential victims and the credit crunch at U.S. banks is making the situation worse.

“With these explosive moves in the commodities a lot of hedgers are exceeding their credit lines and when they go to their banks they can’t get any more credit,” said Phil Flynn of Alaron Trading in Chicago.

Goldman Sachs warned in a research note this month that tight credit was driving leveraged speculators and oil producers with weak credit out of the oil futures market.

Companies closing out short positions on oil may have fueled part of the rally in oil prices this summer, analysts said. Open interest in the NYMEX light sweet crude oil contract has fallen to a 15-month low of 1.3 million contracts, according to Reuters EcoWin data.

Margin calls on oil hedges are not just hitting small companies. Independent refiner Tesoso Corp TSO.N, which holds about 30 million barrels of oil in inventory, in June warned that hedging losses would cost it $125 million this quarter.

Refiners like Tesoro have little option but to hedge their inventory positions because big swings in the price of crude could lead to huge losses. This week’s big slide in oil prices means a 2 million barrel cargo of oil worth nearly $300 million on July 11 would have declined in value by more than $50 million.

OPTION COSTS SURGE

Margin calls on oil futures positions have pushed more hedgers and speculators into the oil options market, but the growing volatility of oil prices has made this a more costly method of hedging.

September crude oil options have surged to price levels that suggest traders are betting on swings of more than 50 percent in oil prices in the wake of a 12 percent plunge in U.S. crude futures since July 11.

The September $125 put option, which gives the holder the right but not the obligation to sell a futures contract at $125 a barrel, jumped $1.64 to $5.10 a barrel on Thursday, according to Reuters data.