Alonso fastest as Mercedes pile on the miles
Fernando Alonso sits in his Ferrari at Jerez racetrack in Jerez on January 30, 2014 during the Formula One pre-season test days - by Jorge Guerrero
In wet conditions following heavy overnight rain, the Spaniard posted a best time of 1min 35.334secs from 55 laps.
Germany's Nico Rosberg was second fastest as he continued to give the Mercedes W05 a thorough workout, completing 91 laps in little over three hours to take the team's overall count past 250 for the week.
McLaren's Kevin Magnussen also built on his impressive start as, after going fastest on his first run with the team on Thursday afternoon, he was down in third after getting another 43 laps under his belt.
However, there was no end in sight to reigning double world champions Red Bull's issues as Australian Daniel Ricciardo could only manage seven laps early in the day to take their tally to the week to just 21.
The problems at Red Bull have been reflected across all the teams using Renault engines as Toro Rosso and Caterham have also struggled this week, whilst Lotus didn't even make it to Jerez due to delays in delivering their car for the new season.
Japanese driver Kamui Kobyashi did, though, manage to get through 42 laps in his first experience of driving the Caterham as he returns to the sport after a year out in 2013.