  We report on the detection of pulsations of three pulsating subdwarf B stars
observed by the TESS satellite and our results of mode identification in these
stars based on an asymptotic period relation. SB 459 (TIC 067584818), SB 815
(TIC 169285097) and PG 0342+026 (TIC 457168745) have been monitored during
single sectors resulting in 27 days coverage. These datasets allowed for
detecting, in each star, a few tens of frequencies, which we interpreted as
stellar oscillations. We found no multiplets, though we partially constrained
mode geometry by means of period spacing, which recently became a key tool in
analyses of pulsating subdwarf B stars. Standard routine that we have used
allowed us to select candidates for trapped modes that surely bear signatures
of non-uniform chemical profile inside the stars. We have also done statistical
analysis using collected spectroscopic and asteroseismic data of previously
known subdwarf B stars along with our three stars. Making use of high precision
trigonometric parallaxes from the Gaia mission and spectral energy
distributions we converted atmospheric parameters to stellar ones. Radii,
masses and luminosities are close to their canonical values for extreme
horizontal branch stars. In particular, the stellar masses are close to the
canonical one of 0.47 M$_\odot$ for all three stars but uncertainties on the
mass are large. The results of the analyses presented here will provide
important constrains for asteroseismic modelling.
