There are many modalities that may be used to enhance heat transfer performance. One of these modes, the embossing of channel walls with dimples and/or protrusions, is a technique which has the advantage of simplicity of fabrication. The assessment of the quality of a geometry-based heat transfer enhancement technique frequently involves the change in pressure drop that accompanies the geometric modification. This realization provides the motivation for the investigation reported here. The focus of this work is the identification of the existence of various sub-regimes within the laminar-flow regime. The investigation was implemented by numerical simulation supplemented by a three-dimensional model of periodic fully developed flow. The selected channel-height Reynolds number range extended from 200 to 800. Within this range, three sub-regime laminar flows were identified: friction-dominated flow, inertial-loss-dominated flow, and the transition between these flows. Another focus of the results was the presentation of patterns of fluid flow and their impacts on the variation of the pressure drop with Reynolds number.