The Swiss rank 19th in EF's English Proficiency Index, which puts Sweden on top, followed by the Netherlands, Denmark, Norway and Finland.
Slovenia (sixth), Estonia (seventh), Luxembourg (eighth) and Poland (ninth) round out the countries where English skills are regarded as very high, based on testing conducted in 2014.
The level of English among adults in Switzerland is rated as “high”, but is lower than in such countries as Austria, Germany and Singapore, as well as Portugal, Romania and Belgium, the report shows.
Libya was ranked the lowest, ahead of Cambodia, Saudi Arabia, Algeria and Iraq.
In the five years EF has produced its index, Switzerland's ranking has steadily dropped each year from 11th in 2011, although fewer countries were compared back then.
Within Switzerland, knowledge of English is significantly higher in German-speaking cantons than in French- and Italian-speaking regions, according to the latest findings.
The study shows that among the major Swiss cities, Zurich has the highest level of English skills, rated “very high”, ahead of Bern, Basel, Geneva and last-placed Lausanne.
The relatively low results in French-speaking Suisse Romande may be influenced by the fact that neighbouring France “stands out in Europe for its low English proficiency”.
The index was based on test results from more than 910,000 adults who took EF's online English tests in 2014.
EF, founded in Sweden but now headquartered in Lucerne, Switzerland, said the average level of adult English proficiency has risen in the world but this increase is far from uniform across countries, regions and age groups.
For more on the study, check here.