Shipowners tend to reduce services, regardless of consequences to shippers, in order to maintain profits in the face of increasing cost for fuel and labour. Speeds reduced by 1 to 1 1/2 knots cause a 16/17 knot cargo liner ship to cut consumption by about 20%, because it is at the higher range of speeds that fuel consumption accelerates significantly. Such measures as reducing speed, curtailing the number of sailings and the number of calls made at ports, as well as not calling at intermediate ports, significantly alters the services available. Reduced speed means longer round voyage times, only partly offset by limiting the number of port calls. Such measures increase space demand and difficulties for shippers.