Among the tools of oil broker Michael F. McDermott's trade is a small plastic draftsman's triangle.

McDermott, a senior vice president at Paine Webber Inc., uses the triangle to draw trendlines on a dense chart of past oil price movements. The chicken scratches on the chart, he hopes, will provide some clue about where oil prices are going next, and the best time to get into or out of the market.

This practice is called "technical" trading, or charting, and it is used in one form or another by most players in the oil futures market. Adherents of technical trading believe that those who know history will be lucky enough to repeat it, and argue that the market consists of little more than a series of repeating cycles. The trick is to figure out what point in a cycle the market is in, and then trade based on what the charts say should happen next. Some charts consider market performance over weeks or months; others look at increments as small as a few minutes.

"You try to use past behavior ... and say, based on past behavior, what would be the outcome?" McDermott said. "In a truly efficient market, technical analysis should tell you what's going to happen."

However, McDermott said with a smile, "This is an art form rather than a science."

Indeed. Technical traders deal in a world of patterns and predictions that seems far removed from the nuts and bolts of the market. They speak of "Elliott wave" and "head and shoulders" patterns -- with "necklines," no less -- and even have specific Japanese names for a variety of "Japanese candle" patterns, so known because they resemble burning candles whose width and "flame height" are considered indicators of future market movement.

The Elliott wave theory, for example, holds that prices always move upward in clusters of five thrusts, punctuated by downturns, before finally falling after the fifth crest. According to a computerized analysis, the third upward thrust is often the longest of the five, never the shortest. A similar theory is used by technical traders in the stock market.

Yet for all the appearance of voodoo, many professional futures brokers argue that technical trading is far more precise than trading on the vicissitudes of rumors, news reports and supply and demand, the other major factors that drive the oil market. Some technical traders say they ignore all data other than the charts, arguing that their patterns incorporate every possible influence on oil prices. War, accident, weather, inflation, government policy -- all the permutations already show up in one chart or another, technicians argue.

According to a 51-page primer on technical trading prepared for its brokers by Shearson Lehman Brothers Inc., the premise underlying technical trading is that "since human nature does not change, it becomes reasonable to expect that behavior, as reflected by price formations on the chart, will repeat. In essence, there is nothing 'new' in the market's movement which hasn't already occurred in the past and will not reappear in the future."

"The technicals are the speedometer," said Peter Beutel, director of Pegasus Econometrics Group, a Hoboken, N.J.-based oil trading and consulting firm. "You can get a good handle on what the feel of the market is."

Technical trading purports to predict market movements over years, months, days or even a few minutes. When a broker peering at a computer screen sees a "cross," he is seeing a point at which the line charting current trading crosses the trendline of past patterns, indicating that the market is turning around just at that moment.

Most traders use a variety of methods to cover different situations. McDermott is fond of the theory known as the "inside day," which claims that the range of crude oil prices in the first hour of trading each day can predict where the price will close. If the market breaks both the high and low ends of that first-hour price range later in the day, the theory goes, the price will wind up closing within the first-hour range when the New York Mercantile Exchange settles at 3:10 p.m. Eighty percent of the time, according to McDermott, it works.

Often, many veteran traders say, the widespread use of technical trading causes movements in the price of oil on the futures market that don't otherwise seem justified by news events or supply and demand statistics. Not unlike the stock market's computerized "program trading" -- a distant relative -- technical trading in oil futures can encourage a herd mentality of buying or selling, experts say.

As a result, some critics argue that technical trading is in effect a self-fulfilling prophecy, since so many traders and brokers are looking at the same charts with similar tools and thus making simultaneous decisions to buy or sell.

"Because it is a self-fulfilling prophecy, you know that when the price gets to $30.50 {for instance}, everybody is going to start selling," said one trader who is not a big fan of technical trading. "Everybody is looking for the same numbers."

"You can only get a few flavors out of these things before you start going in circles," said Cynthia Kase, vice president of commodity risk management at Chemical Bank in New York -- who nonetheless is attempting to develop her own computerized technical oil trading system.

Others argue that technical trading is of much less value in markets as volatile as the current one, in which news reports or rumors can cause huge price swings that the charts may not predict.

"You'd go in there and say, 'we're going to get a pullback of a buck,' " said a trader for a major oil company. "Bull -- it would shoot up three bucks before lunch."

What ultimately makes technical trading so popular is that there is no other objective basis on which to analyze the market. The "fundamentals" -- supply and demand -- can change at any minute, unpredictably. "To trade the fundamentals you have to have the mind of God," Kase said. "Anybody who trades on technicals, you only trade on two things -- time and price."