Motivated by the new auction format introduced in the England andWales electric-
ity market, as well as the recent debate in California, we characterize bidding behavior
and market outcomes in uniform and discriminatory electricity auctions. We ¯nd that
uniform auctions result in higher average prices than discriminatory auctions, but the
ranking in terms of productive e±ciency is ambiguous. The comparative e®ects of
other market design features, such as the number of steps in suppliers' bid functions,
the duration of bids and the elasticity of demand are also analysed. We also consider
the relationship between market structure and market performance in the two auction
formats. Finally, we clarify some methodological issues in the analysis of electricity auctions. In particular, we show that analogies with continuous share auctions are misplaced so long as ¯rms are restricted to a ¯nite number of bids