Assalamualaikum ustaz. What is the ruling for Friday prayer for workers in an oil rig? Some of them have to work for more than three weeks or more consecutively. Furthermore, the total number of workers usually doesn’t reach 40 people. Hope for an explanation.
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions and all those who follow his footsteps until the Last Day.
Friday prayer is one of the syarak commandments that is obligatory to be fulfilled by a mukallaf Muslim and it is an eminence of Islam. There are numerous syarak evidences that mention the sanctioning of Friday prayer and the strict prohibition from leaving it purposefully. Allah SWT states:
يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا نُودِيَ لِلصَّلَاةِ مِن يَوْمِ الْجُمُعَةِ فَاسْعَوْا إِلَىٰ ذِكْرِ اللَّهِ وَذَرُوا الْبَيْعَ ۚ ذَٰلِكُمْ خَيْرٌ لَّكُمْ إِن كُنتُمْ تَعْلَمُونَ
“O you who have believed, when [the adhan] is called for the prayer on the day of Jumu’ah [Friday], then proceed to the remembrance of Allah and leave trade. That is better for you, if you only knew.” 
The above verse is among the evidences of the sanctioning and obligation of Friday prayer. Furthermore, the Friday prayer is among the advantages granted especially for the Prophet Muhammad PBUH’s ummah so that they are able to attain the honours of Friday. 
The Friday prayer is also an honoured worship that has various advantages. Among them, it acts as a weekly remover of sins. From Abu Hurairah RA, the Messenger PBUH said:
الصَّلَوَاتُ الْخَمْسُ، وَالْجُمْعَةُ إِلَى الْجُمْعَةِ، وَرَمَضَانُ إِلَى رَمَضَانَ، مُكَفِّرَاتٌ مَا بَيْنَهُنَّ إِذَا اجْتَنَبَ الْكَبَائِرَ
“The five (daily) prayers and from one Friday prayer to the (next) Friday prayer, and from Ramadhan to Ramadhan are expiations for the (sins) committed in between (their intervals) provided one shuns the major sins.” 
The Friday prayer is obligated for those who fulfil the seven following conditions:
- Reached puberty
- Rational sound mind
- A resident in the place where the Friday prayer is performed
If a person doesn’t fulfil any one of the seven conditions, then Friday prayer is not obligated for him. 
Moreover, scholars of madhhab Syafie has set the condition of the minimum number of congregants for Friday prayer is 40 people or more. It is also the opinion of ‘Ubaidullah bin Abdullah bn ‘Utbah, and one of the narrations of Umar bin Abdul Aziz.  Forty men must fulfil the valid conditions of the Friday prayer (اهل الجمعة) which are men, reached puberty and a resident.  And the total number of 40 congregants must remain from the beginning till the end of Friday.  Among the arguments is a narration from Abd al-Rahman bin Ka’ab bin Malik who stated that the number of congregants for the first Friday prayer in Medina is 40 men. 
In answering the above issue, we state the following:
The commandment to seek sustenance in our lives is undeniable and sometimes one has to work far from one’s family for a long time. This happens to the oil rig workers in order for them to provide for their families.
Among the questions that arise is the issue for Friday prayer for those who are working on an oil rig. Is it obligatory for them to perform Friday prayer or does the obligation is abrogated because they don’t fulfil the valid conditions of Friday prayer?
One should be reminded that the Friday prayer is a fardhu ‘ain for those who fulfil its conditions. Friday prayer on an oil rig doesn’t fulfil the conditions related to the place and beinf a resident.
An oil rig is not a city or village where people gather to perform prayer like a building that gathers the local community made of cement, rock, clay and others. This is based on the final qaul in the fiqh book of madhhab Syafie. 
Likewise, in the issue of the number of congregants where in madhhab Syafie, it is stated that for a Friday prayer to be valid, it must have not less than 40 men who are the Friday peope\le which means they are men, have reached puberty and a resident of the place. A temporary resident but not a resident there isn’t considered as the part of the 40 people who are the valid condition of Friday prayer. 
The same is for the situation of people working on an oil rig for they are considered temporary residents.
According to the above statement, we state that for those who work on an oil rig for an extended amount of time, the ruling for them to perform Friday prayer is abrogated because they do not fulfil the valid conditions of Friday prayer.
Although the ruling of Friday prayer is abrogated, however, they have to perform the Zuhur prayer to replace the Friday prayer that cannot be performed for not fulfilling the valid conditions of Friday prayer. It is also appropriate for one of them to deliver a tazkirah during the prayer. It is to serve as a reminder for the makmum there.
Furthermore, maybe the body of authorities and fatwa committee could discuss this issue comprehensively as well as do a site visit to an oil rig to get a clear picture so that it can be properly understood.