This paper examines the efficiency of the Canadian treasury bill market as measured by the performance of the expectations model of the term structure of interest rates. In particular, market efficiency is shown to depend upon certain institutional features of the treasury bill auction process. Building on past work by B. Campbell and J.W. Galbraith [Oxford Bulletin of Economics and Statistics 59 (2) (1997) 265–284], the paper establishes links between rejections of efficiency and high absolute values of the spread between six- and three-month interest rates. The major contribution of the paper is to then show that a link exists between weeks in which spreads are large and weeks in which accepted auction yields show a large degree of dispersion. The paper discusses the implications of these findings for the term structure literature and for possible auction configurations currently under consideration in Canada and the US.