In this work we perform an experimental characterization of the rheology of hydroxypropyl guar (HPG) solutions. The flow situations investigated are shear rheometry, elongational flow in opposed jets, and flow through porous media. The results of the experiments show that hydroxypropyl guar behaves as a semiflexible molecule in aqueous solutions under elongational flow situations. In shear flows and under semidilute conditions, the HPG solutions have a shear-thinning behavior, whereas in opposed-jets flow they exhibit extension thickening. In porous media flows, semidilute solutions behave as shear thinning, but there is evidence that extension thickening is present. We have developed a technique in which a linear charged-coupled device (CCD) array is used as a retardation detector to measure birefringence profiles in opposed-jets flow. This technique has shown that HPG molecules are stretched in the flow field, which confirms that the HPG molecules are semiflexible. The addition of a cross-linking agent to HPG solutions was found to have a pronounced effect on their flow behavior in extensional flows. Filtered dilute solutions exhibit intramolecular cross links that reduce the apparent viscosity of the solution in both opposed jets and porous media flows. On the other hand, semidilute solutions (as well as filtered solutions of low concentrations) exhibit intermolecular cross links that, in porous media flows, result in a sizable increase in pressure drops.