Temperature distribution over the absorber plate of a parallel flow flat-plate solar collector is analyzed with one- and two-dimensional steady-state conduction equations with heat generations. The governing differential equations with boundary conditions are solved numerically using a control volume-based finite difference scheme. Comparisons of one- and two-dimensional results showed that the isotherms and performance curve, stated in terms of an effectiveness/number-of-transfer-unit relationship, for one-dimensional analysis slightly deviate from that of two-dimensional analysis, particularly under low mass flow rate conditions. In addition, collector efficiency as a function of operating point is computed and presented graphically for different collector configuration and various operating conditions. For general engineering purposes, these performance curves may be used for efficient and optimum design of liquid flat-plate solar collectors.