A method of determining the quality of cross-linked hydraulic fracturing gels in the field was developed at the Alberta Research Council. The method is based on the measurement of the pressure required to push the gel through an orifice. The measurement can be repeated several times in order to quantify transient changes in the theology of the gel. The quality of the gel prepared in the field is quantified by plotting the extrusion pressure vs. shear rate at the orifice. This quality control technique was compared, for certain types of water-based and oil-based gels, to existing techniques based on shear rheometry. The comparison showed that the water-based gels we investigated could be characterized using the gel tester, but not with the existing technology. The oil-based gels we investigated could be characterized better using the existing technology.