Title for each subplot is cutoff in R

Despite my using the oma parameter in R, the title for each subplot is cutoff, is there some other parameter that can be used to display properly?

op <- par(mfrow = c(3,3),
          oma = c(0,0,2,0) + 0.1,
          mar = c(0,0,1,1) + 0.1)

enter image description here

Solution

Try par(xpd=NA): from ?par,

‘xpd’ A logical value or ‘NA’. If ‘FALSE’, all plotting is clipped to the plot region, if ‘TRUE’, all plotting is clipped to the figure region, and if ‘NA’, all plotting is clipped to the device region. See also ‘clip’.