The hybridisation in cyclopropene, cyclobutene, 1-methylcyclobutene, and 3-methylcyclobutene, all containing a double bond in the ring, is considered by applying the method of maximum overlap. The results show a considerable increase in s-contribution for the hybrids forming the double bond. The participation of s-orbitals in the hybrids forming the double bond is larger in cyclobutene than in cyclopropene, an indication that the preference for s-character will be even more pronounced in strain-free systems. The calculated bond overlaps are compared with the experimental bond energies. Instead of assuming the simple proportionality when scaling an overlap, a general linear relationship E=kS–l must be used.