Crystal load capacitance

[shadewind]

I'm trying to figure out what loading caps to use for the crystal oscillator for a TI CC2500 (http://www.ti.com/lit/ds/symlink/cc2500.pdf).

The following formula is the one most commonly seen and the one I'm using: C(L) = (C1 * C2)/(C1+ C2) + C(S)

...where C(L) is the crystal specified load capacitance, C1 and C2 are the values of the loading caps and C(S) is the parasitic capacitance of the board and oscillator pins. The crystal I want to use (http://se.farnell.com/txc/7m-26-000maaj-t/xtal-26-000mhz-18pf-smd-3-2x2-5/dp/1842069) has a load capacitance of 18 pF which would mean C1 = C2 = 31 pF if you, as the data sheet suggests, assume that the parasitic capacitance is 2.5 pF. The closes value would me 33 pF which to me seems very high and there is no such value among the examples at page 50 in the CC2500 data sheet. 18 pF seems like a fairly common value for crystals but I'm wondering if this is too high or if 33 pF is simply a normal value for the caps?