Hydrogen (H₂) gas sensors that are sensitive, rapid-responding, stable, selective, compact, and inexpensive are needed to support the operation of fuel cell-electric automobiles. Palladium absorbs hydrogen to form a hydride (PdH_x) with x saturating at 0.67 and since 1869 it has been known that the electrical resistivity of this hydride increases linearly with x by a factor of 1.8 – 1.9 over the range from x = 0 to 0.67. This property of PdH_x was first exploited for hydrogen sensing by Hughes and Schubert in 1992. As hydrogen gas sensors, Pd thin film resistors are elegant in their simplicity and cheap, but they are much too slow. One solution is to use a Pd nanowire as a resistive H₂ sensor instead of a film. In this talk, we describe a second approach involving palladium (Pd) nanoparticle (NP)-decorated carbon nanotube (CNT) ropes (or CNT@PdNP). In the devices we prepare here, the Pd NPs have a mean diameter below 6 nm and are highly dispersed on the CNT surfaces. Both the Pd NPs and the CNT ropes are prepared by pulsed electrodeposition methods. Such CNT@PdNP ropes produce a relative resistance change 20 - 30 times larger than is observed at single, pure Pd nanowires. Thus, CNT@PdNP rope sensors improve upon all H₂ sensing metrics (speed, dynamic range, and limit- of-detection), relative to single Pd nanowires which heretofore have defined the state- of-the-art in H₂ sensing performance. Specifically, response and recovery times in air at [H₂] ≈ 50 ppm are one sixth of those produced by single Pd nanowires with cross- sectional dimensions of 40 × 100 nm Pd. The LOD_H2 is <10 ppm versus 300 ppm, and the dynamic range (10 ppm – 4%) is nearly twice that afforded by the Pd nanowire. CNT@PdNP rope sensors are prepared by the dielectrophoretic deposition of a single semiconducting CNT rope followed by the electrodeposition of Pd nanoparticles with mean diameters ranging from 4.5 (± 1) nm to 5.8 (± 3) nm. The diminutive mean diameter and the high degree of diameter monodispersity for the deposited Pd nanoparticles are distinguishing features of the CNT@PdNP rope sensors described here, relative to prior work on similar systems.