An alpha-galactosidase and a beta-mannanase produced by the hyperthermophilic bacterium, Thermotoga neapolitana 5068 (TN5068), separately and together, were evaluated for their ability to hydrolyze guar gum in relation to viscosity reduction of guar-based hydraulic fracturing fluids used in oil and gas well stimulation. In such applications, premature guar gum hydrolysis at lower temperatures before the fracturing process is completed is undesirable, whereas thermostability and thermoactivity are advantageous. Hyperthermophilic enzymes presumably possess both characteristics. The purified alpha-galactosidase was found to have a temperature optimum of 100-105 degrees C with a half-life of 130 minutes at 90 degrees C and 3 min at 100 degrees C, while the purified beta-mannanase was found to have a temperature optimum of 91 degrees C and a half-life of 13 h at this temperature and 35 min at 100 degrees C. These represent the most thermostable versions of these enzymes yet reported. At 25 degrees C, TN5068 culture supernatants, containing the two enzyme activities, reduced viscosity of a 0.7% (wt) guar gum solution by a factor of 1.4 after a 1.5-h incubation period and by a factor of 2.4 after 5 h. This is in contrast to a viscosity reduction of 100-fold after 1.5 h and 375-fold after 5 h for a commercial preparation of these enzymes from Aspergillus niger. In contrast, at 85 degrees C, the TN5068 enzymes reduced viscosity by 30-fold after 1.5 h and 100-fold after 5 h compared to a 2.5-fold reduction after 5 h for the control. The A. niger enzymes were less effective at 85 degrees C (1.6-fold reduction after 1.5 h and a 4.2-fold reduction after 5 h), presumably due to their thermal lability at this temperature. Furthermore, it was determined that the purified beta-mannanase alone can substantially reduce viscosity of guar solutions, while the alpha-galactosidase alone had limited viscosity reduction activity. However, the alpha-galactosidase appeared to minimize residual particulate matter when used in conjunction with the beta-mannanase. This could be the result of extensive hydrolysis of the alpha-1,6 linkages between mannose and galactose units in guar, allowing more extensive hydrolysis of the mannan chain by the beta-mannanase. The use of thermostable enzymatic breakers from hyperthermophiles in hydraulic fracturing could be used to improve well stimulation and oil and gas recovery.