Updated from 2:06 p.m. EDT

Crude oil prices tumbled below the $50 a barrel level late Friday, after holding around $51 for most of the session, as a collapse in heating oil and gasoline triggered a major selloff in crude.

The June crude benchmark closed down $2.05, or 5%, to $49.72 in Nymex floor trading. Gasoline closed down 5 cents at $1.49 a gallon.

"This was a phenomenal day; heating oil and gasoline led prices downward most of the day, but suddenly the dam just broke, pulling down crude, and everybody was caught in long positions," said Lex Kern, a Nymex pit trader with MK brokerage.

Also keeping energy prices tight were data showing that the U.S. economy grew in the first quarter at a 3.1% annual rate, the slowest pace in two years, the Commerce Department said Thursday. High energy prices, among other items, helped curb consumer spending.

Friday's economic data were mixed, with personal income and spending higher than expected, as was the personal consumption expenditures index in the report. The Chicago purchasing managers index fell but not as much as expected, while the University of Michigan consumer sentiment index was unexpectedly revised down.

A question repeatedly asked by analysts and economists is when high energy prices will start slowing demand at the pump. Some say Americans are able to stomach the price hikes and will continue to drive despite higher gasoline prices, while others say that a slowdown in demand is closer than people think and is likely to be the key ingredient for bringing down prices in the near future.

Either way, drivers are currently burdened with gas prices over $2 a gallon, holding them back from spending money elsewhere.

"Consumer behavior will probably change when gasoline prices hit about $3 a gallon," said Bill O'Grady, assistant director of market analysis at A.G. Edwards. He compares the current tightness in the energy market to the oil crisis in the late 1970s and early 1980s, when, adjusted to inflation and to the CPI, gasoline prices reached $3 a gallon. "If you look at auto advertisements at that time, you would see smaller cars that promote better gasoline usage," he said.

O'Grady estimates that at some point prices will force consumers to sell their SUVs, use more public transportation and carpool. "We aren't there yet, but this scenario is likely to happen in five to 10 years," he says.

Full-sized SUVs lost 1.2 percentage points of U.S. market share in February and March, and large pickups were down about 2 points, according to The Auto Channel, an auto information Web site. Fuel-efficient compact cars, on the other hand, gained 2.2 points of market share in the same period.

But gasoline retail prices also are weighing on the integrated oil and gas producers. Marketing margins -- the difference between the cost of producing a barrel of crude and the amount charged for gasoline at the pump -- have reportedly been shrinking at the major oil producers. That's a sign that consumers are forcing suppliers to reduce prices at the pump. Higher oil prices do not mean higher pricing power for the integrated companies.

In company news,

ChevronTexaco

(CVX) - Get Report

said its net income for the first quarter rose 4%, but it had lower earnings from its refining and marketing operations. "U.S. refining, marketing and transportation earnings of $58 million decreased $218 million from last year's first quarter," the company said in a statement. "The company's refined-product margins were lower in the 2005 period, primarily for West Coast operations."

In other words, ChevronTexaco was not as profitable at selling its motor fuels to consumers.

Anadarko Petroleum

(APC) - Get Report

, an independent gas and oil production company, said its first-quarter profit rose by 25 percent to $490 million, or $2.05 per share, compared with $392 million, or $1.55 per share, in the year-ago period. This beats analysts' earnings estimates of $2 per share according to Thomson Financial. Revenue rose 5% to $1.53 billion. Shares rose 1.30%, to $73.01.

Based on the growing demand for drilling equipment, analyst James Stone at UBS raised his rating on

Rowan Cos.

( RD) to buy from neutral. "The company's strong niche as the premier driller for harsh environment or ultradeep wells should serve the company well as operators take on more challenging drilling conditions," Stone said in a note. Shares rose slightly by 0.23% to $26.54.

Shares of major oil producers gained.

BP

(BP) - Get Report

gained 0.79%;

Exxon Mobil

(XOM) - Get Report

increased 1.71%;

ChevronTexaco

rose 0.87%; and

Royal Dutch/Shell

(RD)

increased 0.24%.