Abstract: A core holder for a reservoir rock core sample for MR or MRI measurement including a casing and a chamber internal to the core holder, an inlet and an outlet in the core holder for circulating a confining fluid in the chamber, a sample housing in the chamber for containing the core sample, the sample housing including an inlet and an outlet in the sample holder for circulating fluid to and from the sample, and a membrane for isolating the sample from fluid contact with the confining fluid but permitting fluid pressure to be exerted on the sample when the confining fluid is pressurized, the space in the chamber not occupied by the sample housing defining a void space, an RF probe in the void space and at least partially surrounding the sample housing, whereby confining fluid introduced into the chamber circulates in the void space around the RF probe.