Distribution of orbital period ratios of adjacent pair of planets as a function of the orbital period of the inner planet in the vicinity of the 2:1 MMR (top) and 3:2 MMR (bottom). Data obtained from exoplanet.eu. The red circles identify confirmed planets detected by transits or TTV, while the blue circles correspond to recently validated Kepler planets proposed by Morton et al. (2016). Planets discovered by any other method are depicted with open circles. In the top panel, open green circles denote the GJ876 system, while the dashed black circle groups the resonant (or near-resonant) members of HD 73526, HD 82943, HD 155358, and HD 92788.