(FORTUNE Magazine) – In the race to become corporate America's Most Favored Letter, lower-case underdogs "e" and "i" bolted to a surprise lead. Their early sprint is over, however, and it's beginning to look as if capital "X" may be the one with real legs.

This being an American sport, the best way to tell who's winning is to check sponsorships. The formerly renegade "X" has gone high tech: Microsoft will call future Windows and Office versions XP (for "experience"), and the company recently unveiled its videogame console, the Xbox.

"X" has always been popular with fans (Gen X, the X Games, The X-Files, the algebraic unknown), but its recent Xplosion into the corporate lexicon is remarkable--369 trademarks contain the word "Xtreme," as do the XFL, Right Guard Xtreme, and Clairol XtremeFX hair color.

Not everyone thinks that "X" can go the distance. "Because 'X' has become so diluted, it's going to disappear more quickly than 'e' and 'i,' which are slowly fading away," says Ira Bachrach of NameLab. What will supplant "X"? Bachrach thinks "dj" (as in "wouldja") and "GR8" (hacker shorthand for "great") will be the Next Big Things.

--Grainger David