The spectra of energetic electrons produced by a laser interaction with underdense plasma have been measured at intensities $>3\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{W}\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$. Electron energies in excess of 300 MeV have been observed. Mea...