An oilfield servicing fluid composition containing an aldehyde guar produced by enzymatic oxidation of a non-derivatized, straight guar or of a guar derivative. The enzyme used to oxidize the guar to the aldehyde guar is galactose oxidase, which may be combined with catalase or catalase and peroxidase. The aldehyde guar is useful as an effective gelling agent for oilfield servicing fluids such as hydraulic fracturing fluids and stimulation fluids.