(1)	$\begin{array}{l}\displaystyle c = c(p)\end{array}$

The multi-phase compressibility is a linear sum of compressibilities of its phases.

Approximations

Incompressible fluid

(2)	$\begin{array}{l}\displaystyle c(p) = 0\end{array}$

(3)	$\begin{array}{l}\displaystyle c(p) = \rm const\end{array}$

(4)	$\begin{array}{l}\displaystyle c(p) = \frac{1}{p}\end{array}$

(5)	$\begin{array}{l}\displaystyle c(p) = \frac{c_0}{1+c_0 \cdot p}\end{array}$