Through 2006, the dominant players in the hybrid market remained pioneers Toyota and Honda, although that will be changing rapidly with many new introductions of hybrid vehicles from other manufacturers, including all of the US automakers. The increased initial cost of hybrids is likely to limit their long-term appeal to half of the market or less unless they continue to receive incentives like tax breaks. If you want to read the full report it will cost you about €1,070 for an electronic copy.
UPDATE: As readers have noted in the comments, one reason for high U.S. hybrid sales is Europe's fascination with diesel the U.S. doesn't get, like this one.
[Source: Research and Markets]