The efficiency of the dimethyl ether (DME) enhanced oil recovery (EOR) technique in a fractured chalk reservoir core plug was investigated. The coreflood experiment showed that DME EOR could lead to 44.2% additional oil recovery, amounting to 80.6% of the ultimate oil recovery. A comprehensive set of laboratory experiments, including density measurements of miscible fluids, DME-induced oil swelling factor, and partition coefficient of DME between the aqueous and oleic phase, were performed. The experimental results show that the partition coefficient of DME for the mixture of DME-brine-oil can reach up to 18.3. The oil swelling factor for such a system can reach up to 2.7 under realistic reservoir conditions. Comparing this data set to the available data for other mutually soluble solvent-based EOR techniques shows that the oil swelling caused by DME is far stronger than for other common solvents. Due to the strong partitioning of DME between the phases, the DME from the DME-brine solution rapidly partitions into the bypassed oil in the low permeability matrix, which leads to strong oil swelling and production.