Abstract. The production function is explaining the mechanism through which inputs are changed into outputs and the partial efficiency of labour and capital. It also allows for understanding the elasticity of substitution, which measures the percentage change in factor proportions due to a percentage change in the marginal rate of technical substitution. In this study we have applied the two factor Constant Elasticity of Substitution (CES) production function, which is considered to be the generalised form of the Cobb-Douglas function. Using the available statistical data regarding Romania's economy in 1990-1005 period, we have performed time-series and cross-section analysis based on the aggregated production functions at national level.

Keywords: production function; elasticity of substitution; Cobb-Douglas, CES, capital and labour.