variavel0=<b>J. C. M. Palhares</b> - palhares@tbg.com.br TBG
<b>A. F. Orlando</b> - afo@mec.puc-rio.br PUC-Rio
<b>M. N. Frota</b> - mfrota@mec.puc-rio.br 
<b>Abstract.</b> The purpose of this paper is to evaluate the present natural gas flow rate measurement procedure in Bolívia-Brasil gas pipeline facilities. Although the transported volumes are less than on third of the pipeline capacity, the mass balance metrology already points out the necessity of improvements clearly aiming to reducing the measurement uncertainty. The mass balance measurement uncertainty has several functions: 1) to drive investments in order to reevaluate or improve less accurate measurement systems; 2) to point out the right moment when to investigate and control eventual gas losses; 3) to participate in determination of line packing; 4) to help in gas pipeline advanced systems like leak detection and simulation of operational conditions; 5) to support sale and purchase contracts as well as gas transport contracts. The present work demonstrates that a consistent metrological evaluation of the transported and consumed gas, contributes definitely to the reduction of unaccounted gas, to improving contracts and improving operational control. Furthermore, it estimates more accurately the natural gas volumes, thus minimizing financial losses, being an instrument to be used for adapting the measurement system to the existing custody transfer legislation.
<b>Keywords.</b> Gas, Pipeline, Flow, Mass Balance, Custody Transfer.