In a computer system having multiple processing units, a method of ray tracing multiple rays in parallel in a computer-represented environment that includes multiple geometric objects enclosed in a bounding volume hierarchy, BVH, the method comprising, for each of multiple threads of one of the multiple processing units: receiving (410, 41n) one or more parameters for a given ray among the multiple rays, wherein the one or more parameters include a distance to a leading intersection for the given ray, which is the closest intersection to an origin of the given ray found so far for the given ray; and traversing (420, 42n) the BVH to determine an intersection, if any, between the given ray and a given geometric object among the multiple geometric objects of the BVH, wherein order of traversal of the BVH is synchronized between the multiple threads for the multiple rays, the traversing including, in each of multiple iterations for each of the multiple threads: loading a bounding volume for a given node of the BVH; for the given ray, testing the bounding volume for the given node; determining whether to continue the traversing within the bounding volume for the given node based on a cross-group operation in order to synchronize the traversal of the BVH between the multiple threads for the multiple rays, including determining, based on results of the cross-group operation, whether the bounding volume includes, for any of the multiple rays or for at least a threshold number of the multiple rays, any new intersection closer to the ray origin than the leading intersection for the given ray; and if it is determined that the bounding volume includes, for any of the multiple rays or for at least a threshold number of the multiple rays, any new intersection closer to the ray origin than the leading intersection for that ray, continuing the traversing within the bounding volume for the given node. receiving (410, 41n) one or more parameters for a given ray among the multiple rays, wherein the one or more parameters include a distance to a leading intersection for the given ray, which is the closest intersection to an origin of the given ray found so far for the given ray; and traversing (420, 42n) the BVH to determine an intersection, if any, between the given ray and a given geometric object among the multiple geometric objects of the BVH, wherein order of traversal of the BVH is synchronized between the multiple threads for the multiple rays, the traversing including, in each of multiple iterations for each of the multiple threads: loading a bounding volume for a given node of the BVH; for the given ray, testing the bounding volume for the given node; determining whether to continue the traversing within the bounding volume for the given node based on a cross-group operation in order to synchronize the traversal of the BVH between the multiple threads for the multiple rays, including determining, based on results of the cross-group operation, whether the bounding volume includes, for any of the multiple rays or for at least a threshold number of the multiple rays, any new intersection closer to the ray origin than the leading intersection for the given ray; and if it is determined that the bounding volume includes, for any of the multiple rays or for at least a threshold number of the multiple rays, any new intersection closer to the ray origin than the leading intersection for that ray, continuing the traversing within the bounding volume for the given node. loading a bounding volume for a given node of the BVH; for the given ray, testing the bounding volume for the given node; determining whether to continue the traversing within the bounding volume for the given node based on a cross-group operation in order to synchronize the traversal of the BVH between the multiple threads for the multiple rays, including determining, based on results of the cross-group operation, whether the bounding volume includes, for any of the multiple rays or for at least a threshold number of the multiple rays, any new intersection closer to the ray origin than the leading intersection for the given ray; and if it is determined that the bounding volume includes, for any of the multiple rays or for at least a threshold number of the multiple rays, any new intersection closer to the ray origin than the leading intersection for that ray, continuing the traversing within the bounding volume for the given node.