NOVELTY - The method (20) involves conveying (21) a carrier through the borehole. Formation measurements are performed (22) in relative to the porosity at depths of borehole, using a downhole tool. Upper and lower depth intervals are defined (23), where the intervals have a set of formation measurement points. Multiple trendlines of depth versus porosity-related measurements are established (24) using a processor, where the trendlines extend from upper depth interval to lower depth interval. Pore pressure line and associated uncertainty are calculated (25) using trendlines.    USE - Method for estimating pore pressure of earth formation penetrated by borehole and associated uncertainty, used in hydrocarbon production, geothermal production and carbon dioxide sequestration.    ADVANTAGE - As the depth intervals are shifted or widened and more formation measurement points are obtained, several trendlines are established, hence the pore pressure line and the associated uncertainty are determined effectively without damaging equipment so as to reduce the delay cost. The transferability characteristics between the locations of the boreholes are represented, by applying the weighting function while porosity-indicating logs originate from different locations.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) an apparatus for estimating a pore pressure of earth formation penetrated by borehole and associated uncertainty; and    (2) a non-transitory computer-readable medium storing program for estimating pore pressure of earth formation penetrated by borehole and associated uncertainty.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart illustrating the method for estimating pore pressure of earth formation penetrated by borehole and associated uncertainty.    Step for estimating pore pressure of earth formation penetrated by borehole and the associated uncertainty (20)    Step for conveying a carrier through the borehole penetrating an earth formation (21)    Step for performing formation measurements in relative to the porosity at depths of the borehole, using the downhole tool coupled to the carrier (22)    Step for defining the upper and lower depth levels with upper and lower set of formation measurement points respectively (23)    Step for establishing the trend lines of the depth versus porosity-related measurements using the processor (24)    Step for calculation of the pore pressure line and the associated uncertainty using the trendlines (25)