Platts officially launched its Americas Sour Marker, or ASM, on Monday in a bid to create a better crude pricing mechanism than the existing West Texas crude futures contract currently maintained by the New York Mercantile Exchange.

Platts, a division of McGraw-Hill ( MHP) and a leading publisher of energy data and analysis, says that the ASM will represent a blend of sour crudes that are delivered to import terminals in the U.S. Gulf of Mexico.

The Nymex's West Texas crude oil contract represents light sweet crude with a delivery point near the Cushing, Okla., hub. Platts says that the ASM will be a better indicator of global crude oil prices because the Gulf coast is more exposed to international crude markets than WTI at the landlocked Cushing hub.

Furthermore, the amount of sour crude that the U.S. uses to produce refined products like motor gasoline has been steadily rising, while light sweet crude use is on the decline.

The Nymex has been defending the validity of WTI as a global pricing mechanism for crude oil. "The liquidity and transparency provided by WTI is unmatched by any existing or proposed marker," said Anu Ahluwalia, associate director of communications for the CME Group ( CME), which owns the Nymex.

Because sour crude is more expensive to refine than light sweet crude, the ASM should have a natural market price that is slightly lower than the WTI contract at the Nymex. However, this relationship can change freely depending on market conditions.

If the ASM were to take market share from WTI as a pricing mechanism, traders would likely see a modest decline in average crude oil prices. In the short run, this would likely weigh on oil and gas stocks like BP ( BP), Chevron ( CVX), ConocoPhillips ( COP) and Exxon Mobil ( XOM).

However, some analysts doubt that the ASM will ever progress beyond a metric that Platts publishes along with hundreds of other commodity prices.

"Unless the Platts ASM benchmark is a tradable contact on a platform like the Nymex or the ICE Exchange, it will never become a replacement for WTI," says James Williams, energy economist at WTRG economics.