Modular in-line fluid regulators are described. One described example modular fluid regulator apparatus includes a body having a fluid inlet and a threaded outer surface to engage a threaded opening in another fluid regulator to serially fluidly couple first and second fluid regulators. The example fluid regulator apparatus also includes valve to control a flow of fluid through the first fluid regulator, and a pressure sensing member operatively coupled to the valve to control a position of the valve to provide a regulated output pressure at an outlet of the first fluid regulator. The pressure sensing member and the valve are configured to be received in a cavity of the second fluid regulator adjacent the threaded opening.
