What do you mean by "due to pressure increasing"?
it is a little difficult for me to explain, this explanation is from General Chemistry, 8th edition, Martin Silberberg page 243:
"2. Effect of particle volume. At normal Pext, the space between particles (free
volume) is enormous compared with the volume of the particles themselves (particle
volume); thus, the free volume is essentially equal to V, the container volume in PV/RT.
At moderately high Pext and as free volume decreases, the particle volume makes up
an increasing proportion of the container volume (Figure 5.25). At extremely high
pressures, the space taken up by the particles themselves makes the free volume
significantly less than the container volume. Nevertheless, we continue to use the
container volume for V in PV/RT, which causes the numerator, and thus the ratio, to
become artificially high.
This particle volume effect increases as Pext increases, eventually
outweighing the effect of interparticle attractions and causing PV/RT to rise
above the ideal value."
I think it means that we assume the volume for ideal gas and real gas the same, and now I am wondering if the volumes are the same so why do the curves rise above the ideal gas line where PV/RT=1, I'm not sure but I guess although we assume the same value for the volumes, but in real gas pressure must be higher due to reduced volume (which we neglect in PV/RT)