  We propose a two parameter ratio-product-ratio estimator for a finite
population mean in a simple random sample without replacement following the
methodology in Ray and Sahai (1980), Sahai and Ray (1980), Sahai and Sahai
(1985) and Singh and Ruiz Espejo (2003).
  The bias and mean square error of our proposed estimator are obtained to the
first degree of approximation. We derive conditions for the parameters under
which the proposed estimator has smaller mean square error than the sample
mean, ratio and product estimators.
  We carry out an application showing that the proposed estimator outperforms
the traditional estimators using groundwater data taken from a geological site
in the state of Florida.
