Communication: The efficiency of organic field-effect transistors (OFETs) based on high-purity alpha-octithiophene (alpha-ST) and its alkylated derivative DH alpha-8T (see Figure) has been investigated, particular attention being paid to the influence of oligomer length, material purity, and film ordering on OFET performance, especially field effect mobility. The question of whether the mobility of the oligothiophenes keeps on increasing with chain length is discussed.