  We report measurements of the magnetic penetration depth $\lambda$ in single
crystals of PrOs$_{4}$Sb$_{12}$ down to $\sim$0.1 K using a tunnel-diode based,
self-inductive technique at 21 MHz, with the ac field applied along the
\textit{a}, \textit{b} and \textit{c} directions. In all three field
orientations the penetration depth and superfluid density $\rho_{s}$ tend to
follow a power law, $\lambda \sim \mathit{T}^{2}, \rho_{s} \sim \mathit{T}%
^{2}$ at low temperatures. $\rho_{s}$ for various gap functions have been
calculated, and data is best fit by the $^{3}$He A-phase-like gap with
multidomains, each having two point nodes along a cube axis, and parameter
$\Delta_{0}$(0)/\textit{k}$_{B}$\textit{T}$_{c}$ = 2.6. This suggests that
PrOs$_{4}$Sb$_{12}$ is a strong-coupling superconductor with two point nodes on
the Fermi surface. We also confirm the observation of the double transitions at
1.75 K and 1.85 K seen in other measurements.
