Before revision:  We study four models including the variants of Frank, Gumbel , Clayton copulas and find that the non-exchangeable Gumbel copula describes the data distribution and correlation very accurately .
After revision:  We employ four models for the production copula, that is, trivariate versions of Frank, Gumbel , Clayton copulas and find that the non-exchangeable Gumbel copula describes the data distribution and correlation very accurately .