We develop a new analysis of sampling-based motion planning in Euclidean space with uniform random sampling, which significantly improves upon the celebrated result of Karaman and Frazzoli (2011) and subsequent work. Particularly, we prove the existence of a critical connection radius proportional to Θ(n −1/d ) for n samples and d dimensions: Below this value the planner is guaranteed to fail (similarly shown by the aforementioned work, ibid.). More importantly, for larger radius values the planner is asymptotically (near-)optimal. Furthermore, our analysis yields an explicit lower bound of 1 − O(n −1 ) on the probability of success. A practical implication of our work is that asymptotic (near-)optimality is achieved when each sample is connected to only Θ(1) neighbors. This is in stark contrast to previous work which requires Θ(log n) connections, that are induced by a radius of order log n n 1/d . Our analysis is not restricted to PRM and applies to a variety of "PRM-based" planners, including RRG, FMT * and BTT. Continuum percolation plays an important role in our proofs. Lastly, we develop similar theory for all the aforementioned planners when constructed with deterministic samples, which are then sparsified in a randomized fashion. We believe that this new model, and its analysis, is interesting in its own right. not exist, most have the desired property of being able to find a solution eventually, if one exists. That is, a planner is probabilistically complete (PC) if the probability of finding a solution tends to 1 as the number of samples n tends to infinity. Moreover, some recent sampling-based techniques are also guaranteed to return high-quality solutions that tend to the optimum as n diverges-a property called asymptotic optimality (AO). Quality can be measured in terms of energy, length of the plan, clearance from obstacles, etc.An important attribute of sampling-based planners, which dictates both the running time and the quality of the returned solution, is the number of neighbors considered for connection for each added sample. In many techniques this number is directly affected by a connection radius r n : Decreasing r n reduces the number of neighbors. This in turn reduces the running time of the planner for a given number of samples n, but may also reduce the quality of the solution or its availability altogether. Thus, it is desirable to come up with a radius r n that is small, but not to the extent that the planner loses its favorable properties of PC and AO.