Chemical gas dispersion can represent a severe threat to human and animal lives, as well as to the environment. Constructing a map of the distribution of gas in a fast and reliable manner is critical to ensure accurate monitoring of at-risk facilities and coordinate targeted and swift rescue missions when an emergency occurs. In recent years, robots have been endowed with gas sensing capabilities, and several algorithms to generate gas maps have been studied, often producing a 2D map. Two of the major drawbacks of these studies are concerned with the fact that the robot’s path is often fixed to a predefined route, and that the tridimensionality of the gas dispersion phenomenon is not captured by the final gas maps. In this letter, we study the effect of a random walk and an adaptive path planning approach based on informative quantities to gas mapping in a 3D environment using a micro aerial vehicle with severe flight time constraints. We also introduce a clustering strategy to enhance the exploration of the environment. The strategies are compared to a lawnmower movement and evaluated against a ground truth map of the environment, both in simulation and with physical experiments, in order to assess which ones are able to provide an accurate gas map, while simultaneously achieving satisfactory coverage of the desired volume under time constraints.