We demonstrate highly quick response and long distance distributed oil
sensors using a newly developed eccentric core fiber (ECF). This dist
ributed oil sensor, based on an interaction between measurand oil and
evanescent-wave from the ECF, has achieved as short as 4 minutes respo
nse time by using an improved coating material and a sensing length ov
er 17 km at a signal wavelength of 1310 nm. The observed sensitivity c
haracteristics coincide with the calculations of the evanescent power
outside the cladding and it is shown that the sensitivity can be well
estimated From the amount of the outer cladding component of the evane
scent power.