  We discuss the expansion of the universe in the FRLW model assuming that the
source of dark energy is either tachyonic scalar field or quintessence. The
tachyonic scalar field with exponential and power-law potential (function of
homogeneous scalar field $\phi$) both gives exponential expansion of the
universe. It is found that this behaviour is not distinguishable from the
quintessence with respect to these potentials.
