A system for performing inline measurements of flow rate, density, and rheology of a flowing fluid is disclosed, comprising: (a) a rheology measurement subsystem comprising: a horizontal tube of internal radius rH; means for measuring a velocity profile of a test fluid flowing through said horizontal tube at a distance x0 from its upstream end; and means for determining wall shear stress at a boundary between said flowing fluid and an inner surface of said horizontal tube; (b) a density measurement subsystem comprising: a vertical tube of internal radius rV in fluid connection with said horizontal tube; a pressure sensor for measuring the pressure of said test fluid within said vertical tube at a location y1; and, (c) a pressure sensor for measuring the pressure of said test fluid within said vertical tube at a location y2 downstream from y1 and displaced vertically from y1 by a distance Δh.