Billera, Jia and Reiner defined a quasi-symmetric function invariant for matroids. Although powerful, this invariant does not specialize to the Tutte polynomial. In my talk I will define a quasi-symmetric function for every matroid, or more generally, polymatroid. This invariant will specialize to the Billera-Jia-Reiner quasi-symmetric function, as well as the Tutte polynomial. Like the Billera-Jia-Reiner quasi-symmetric function it has the valuative property for (poly)matroid base decompositions. In fact, I conjecture that my invariant is universal with this property.