The activity of commercial cellulases extracted from Trichoderma viride and Aspergillus niger on carboxymethylcellulose and Avicel generally increased at high pressure up to 500 MPa (above atmospheric pressure) [130]. The activity of cellulases from Aspergillus niger was assessed on carboxymethylcellulose in 10% [BMIM][Cl] at 30°C at hydrostatic pressures up to 675 MPa (above atmospheric pressure). The activity increased by 70% at a pressure of 100 MPa, compared to the activity at atmospheric pressure; then decreased for pressures above 200 MPa. The activity at 600 MPa was comparable to the one at atmospheric pressure. Although the cellulases lost 50% of their activity in 10% [BMIM][Cl] at atmo­spheric pressure, their activity in 10% [BMIM][Cl] at 100 MPa is about 85% of the one in acetate buffer at atmospheric pressure. This result suggests that high pressure can limit the de-activation of cellulase in ILs [123].