A preview of the planned replacement for the Alero was seen in 2001 with the unveiling of the Oldsmobile O4 concept, designed by Bertone. The car was an open top 4-seater with European styling but some Oldsmobile traits, and powered by the latest Ecotec I4 engine. The name had multiple meanings, including "Oldsmobile 4-Seater" as well as implying the year 2004 as a planned date for production.

Unfortunately, the O4 concept was unveiled a few weeks after General Motors announced that they would be phasing out the Oldsmobile brand, meaning that production possibilities of the O4 would never become reality. Because of this, a second generation Alero was never built and the car was phased out with the Oldsmobile brand in 2004.

Source: Wikipedia, 2011