Oxygen-enhanced ΔT1 tumor measurements were feasible in 12/22 colorectal cancer patients by means of single-slice MOLLI. A small but statistically significant negative tumor ΔT1 was found overall, in line with the expected response in well perfused and oxygenated tissue [mean (95% CI) ΔT1 = -33 (-41, -25) msec; mean tumor T1 = 1545 ± 163 msec]. A significant negative MOLLI ΔT1 was found in muscle. Repeatability and interobserver agreement were acceptable. Multi-slice variable-flip-angle VIBE tumor T1 measurements were degraded by motion or susceptibility artefact. Technical developments aimed at mitigating artefact and amplifying ΔT1 are needed for future clinical translation.