TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractXanthan gum has been used extensively as a viscosifier in the oil industry for different applications due to its unique rheological properties. In this paper we describe the properties of two previously introduced bio-polymers for use in drilling, drill-in, completions, spacer fluids and coiled tubing applications. The first bio-polymer yields higher viscosities and better temperature stability at lower polymer concentrations than welan and xanthan gum due to its higher molecular weight; this polymer is particularly effective in low salt fluids. The second bio-polymer has improved solubility in high density CaCl 2 brines.Viscosity data over a wide shear rate range in different brine systems is presented comparing the new bio-polymers with xanthan and welan gum at temperatures between 75 o F to 330 o F. The effect of different types of solids and friction pressure tests in coiled tubing are presented, showing diutan's friction reduction properties.