The use of hole opening tools in conjunction with Rotary Steerable Systems (RSS) has increased dramatically in the past few years. Although excellent performance has been delivered with the mainstream commercial tools, alternate options have been developed to enable an RSS to drill the pilot hole in conjunction with a string tool to open the hole in a single run. The most popular current option involves a weight or hydraulic activated underreamer. However, fixed blade, multi-diameter reaming tools have recently been developed for use within Rotary Steerable (RS) assemblies:An eccentric string reamer that will pass through a small pilot hole but then drill and produce a larger hole. This provides a significantly lower-cost hole opening option.A concentric string reamer that utilizes a tapered design incorporating a mid and main reamer section. This innovative design uses a mid-reamer that enlarges the pilot hole to an intermediate size and stabilizes the main reamer above it on its gauge pads. Because of its unique design, the mid reamer is able to stabilize the tool even if the pilot hole is of poor quality or is overgauge. This is particularly beneficial with RS tools in soft formations, leading to improved borehole quality and BHA stabilization. It also enables the use of smaller RS tools, thus providing greater directional potential. Additionally, a single RSS can be used to drill multiple hole size intervals, minimizing BHA changes, which in turn increases rig floor safety and lowers costs. Several distinct applications are documented where these fixed bladed solutions, in combination with both Push and Point RS tools, have proven extremely successful. This has provided greater flexibility with regard to tool selection and well planning options, delivering lower cost per foot in RS projects. Case studies are presented from the Far East, Norway, and the Gulf of Mexico. Introduction Hole opening tools fall into two main categories; Eccentric and Concentric. Eccentric reamers are fixed reamers that are dominated by bicenter drill bits or 'wing-like' string reamer tools using PDC cutters. They are developed for applications where hole enlargement is required but the tool has to pass through a smaller diameter restriction than the required final hole size. The concentric tools are more diverse and consist of fixed designs such as concentric drill bits and string tools (that could be either PDC or roller cone cutting structures), to more complex tools that open on demand by either mechanical or hydraulic control. The growth in the use of hole opening devices over the last few years was driven predominantly by the growth of deepwater drilling. The lessons learned from innovations in the deepwater have extended those applications to shallower waters and even to selected land wells. Hole opening while drilling devices have enabled operators to set larger strings of casing deeper in holes where hole stability, lost circulation and high-pressure zones are a constant problem. This has the obvious advantage of eliminating trips while leaving sections of open-hole exposed over shorter durations, as well as providing a larger annulus for better cement jobs. The ability to reach extremely deep reservoirs with 12 1/4", 10–5/8", and 8 ½" well bores enables operators to run larger and more complex production strings, and this in turn has had an enormous impact on exploration and production economics.