BART and Ghirardelli staff will hand out chocolate squares and coupon cards to thank customers for riding BART and doing their part to unclog the freeways and reduce pollution.
The giveaway is valued up to an estimated $1 million, according to BART.
BART officials say they selected Ghirardelli to be part of their end-of-year thank you events because they believe the company is synonymous with the San Francisco Bay Area.
Ghirardelli officials say they eagerly vied to be one of BART's holiday partners because there's nothing more festive than their decadent, slow-melting, rich chocolate.
The company said it wants BART riders to be some of the first customers in the nation to indulge in their newest flavor: milk chocolate with peanut butter filling.
Some 50,000 peanut butter-filled chocolate squares and cards will be distributed 6 a.m. to 9 a.m. at BART's Downtown Berkeley, Oakland City Center/12th Street stations as well as four stations in San Francisco: Embarcadero, Montgomery Street, Powell Street and Civic Center.
The free cards each contain three coupons that riders can redeem either at Ghirardelli retail stores, a regular grocery or drug store or on-line.
BART officials say the rider appreciation event won't cost riders or taxpayers a cent and is made possible by a $1 million donation by Ghiradelli.
BART spokesman Linton Johnson will be at BART's Oakland City Center/12th Street station at 5:30 a.m. for media interviews where reporters can capture the reaction of riders as they receive the Ghirardelli goodies.
Ghirardelli Senior Vice President of Marketing Fabrizio Parini will be available at the Embarcadero Station in San Francisco.