The kinetics of unidirectional viscous-gravity spread of oil is addressed for the case where oil is discharged at a constant rate on a calm water surface. A new experimental setup is used along with the order-of-magnitude approach to study the dynamics of spreading. Experimental results are consistent with the order-of-magnitude-analysis based spreading-law expression and, in addition, yield the prefactor needed in this expression. Results also provide the accuracy of the constant-volume-based approximation for the spreading rate.