In this work we achieve C polarization levels higher than those reported for dDNP experiments, although we note that dDNP could produce fumarate solutions with higher molar polarization since the [1,4-13 C2]-isotopomer can be used with both carbons in principle polarized up to 100%. When fumarate is formed from parahydrogen, the proton singlet state can be converted into 100% polarization of the C spin in the [1-13 C] isotopomer (an AA'X spin system), or 50% polarization of each C spin in the [1,4-13 C2] isotopomer (an AA'XX' spin system) .