Natural rock deformation is characteristically heterogeneous on all scales. Through experimental deformation of a typical oolitic limestone, under upper crustal conditions, an attempt is made to evaluate the relative influences of temperature and strain rate upon the promotion of strain homogeneity. The material used was selected on the basis of such criteria as a simple diagenetic history and an absence of previous strain history. This approach leads to the expectation that the rock in question, a Mesozoic limestone from the Oolite Series of the British Jurassic, might be realistically comparable to the condition of relatively young carbonate rocks in such structures as the Helvetic nappes of the European Alps at their time of deformation. Accordingly, specimens of oolitic limestone were deformed at a common confining pressure of 200 MPa, at temperatures of 25°, 100° and 200° C, and at strain rates extending over three orders of magnitude from 10 −4 to 10 −6 sec −1. Subsequent strain analyses were made on photographic enlargements of thin sections of the whole of each deformed sample cut in the plane containing the maximum and minimum dimensions of the distorted ooids. A qualitative view of the degree of strain heterogeneity is obtained by contouring strain variability and fully quantitative measure is obtained by expressing the degree of shape fluctuation as a coefficient of determination obtained from the leastsquares fit of the ooid axial data. For samples shortened to 40% at a strain rate of 10 −4 sec −1, the homogeneity coefficient ( r 2) ranged from 0.17 (25°C) to 0.42 (200°C), whereas at the slower rate of 10 −6 sec −1, the coefficient ranged from 0.56 (25°C) to 0.73 (200°C). Under all circumstances, but especially at temperatures above 100°C, strain rate is very much more effective than temperature in promoting a higher degree of strain homogeneity.