We propose a method for calculating the cuttings (solids) concentration in the annular space and the equivalent circulating density (ECD) in deepwater drilling, both in the pilot hole drilling step and in the reaming step. We have found that drilling a pilot hole followed by reaming has certain advantages over drilling with no pilot hole. When using technology involving preliminary drilling of a pilot hole, the solids concentration in the annular space and the equivalent circulating density are reduced.