Undersaturated oil formation volume factor	B_o (p)	bbl/stb	$\begin{array}{l}\displaystyle B_o(p) = 1 + a_1 \, R_s(p) + (T-60) \, \left( \frac{\gamma_{API}}{\gamma_g} \right) \, \big[ a_2 +a_3 \, R_s(p) \big]\end{array}$

where

$\begin{array}{l}p\end{array}$	psia	Fluid pressure
$\begin{array}{l}T\end{array}$	°F	Initial formation temperature
$\begin{array}{l}\gamma_{API}\end{array}$	°API	Oil API gravity
$\begin{array}{l}\gamma_o\end{array}$	frac	Oil specific gravity
$\begin{array}{l}\gamma_g\end{array}$	frac	Gas specific gravity

and

	$\begin{array}{l}\gamma_{API} \leq 30 \ {\rm API}\end{array}$	$\begin{array}{l}\gamma_{API} > 30 \ {\rm API}\end{array}$
$\begin{array}{l}a_1\end{array}$	4.677 · 10^-4	4.670· 10^-4
$\begin{array}{l}a_2\end{array}$	1.751· 10^-5	1.100· 10^-5
$\begin{array}{l}a_3\end{array}$	-1.811· 10^-8	1.337· 10^-9

References

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