The lines were operated by Comboios de Portugal and maintained by REFER (or the predecessor CP).
The majority of railway lines in Portugal were built to 1,668 mm (5 ft 5+21⁄32 in) Iberian gauge.
To reduce construction costs, some lines (notably in rural and mountainous parts of the country) were built to narrow gauge.
The Série 9700 diesel multiple units were purchased secondhand from the Yugoslav Railways in 1980, but frequently proved unreliable.
Media related to Narrow gauge railways in Portugal at Wikimedia Commons